Altimetry
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Altitude, altimetry and altimeters. Altitude as a concept. Barometric and radio altimetry.
Accident - Aeroperú Flight 603, Dambusters.
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Transcripts are approximate. Email us if you have any questions.Transcript Start
00:03
Sam, Adam, Altimetry. What do you know? Well, I feel like I know a lot. Why? Because it's in our everyday life, okay, but then I also feel like I don't know as much as I should. And when it gets very technical, I don't really, you know, this just things that are more clear to understand it.
00:22
Yeah. Maybe. But obviously, then this is not so much about the technical side of it that we're gonna talk about. Do you think the scope of this is big or? Yeah? I think so. I think you could go on a lot of tangents with our altimetry and altimetres, okay?
00:36
It kind of touches on instrumentation and pressure. Where should we stop? I thought maybe the different types of altimeter. Okay. I thought of three that we use commercially three different types. Can you think of any more? I'd say if I can think of three, but I was thinking the barometric altimeter, obviously, the GPS altimeter, which we don't really use, but is there and then the radio altimeter, yeah, as well.
01:04
And maybe just explaining the differences and how we would use them differently and what they used for. Should we talk about? Pressure altimetry barometric? Yeah, sounds good. It might be the main source of altimetry. Yeah that's generally what we use primarily? Listen to. But what is your altitude?
back to topAltitude
01:24
Yeah. What does that mean? Well, it is obviously your height above sea level based on standard atmospheric pressure. I feel like if mixed of a few things that yes probably I'm sure when I was doing my research I read some Latin like definition of oh yeah I'll team metre or I'll really yeah but I'm interested.
01:51
I can't remember. Yeah. Sorry, well I mean I think you can distil this to the basics which is do we ever really know what our altitude is? Well, yes, sort of. Okay, this is, yeah, with the radio altimeter. Okay, good point, but not so much with the barometric. I agree.
02:15
What do we want to know our altitude with reference to? Yeah, and the core of it being what is an instrument in the cockpit. What is it? Really telling you? Yeah. Okay. And after staring at it for 30 years or 50 years or how long you career might be, what does your brain think?
02:39
It's telling you do we need to always be aware of the limitations of everything that instrumentation the aircraft, especially these things that were staring at. Yeah, all day, every day. Yeah, because I feel like after thinking long and hard about altimeters I've realised. It's more of a concept than like a.
03:02
Yeah yeah and an absolute thing. Yeah, I agree. So you like to tell everybody, were at 3,000 feet feel so secure. It's like I got three zero zero. Yeah. But where am I? Really? How? How high yeah. What exactly is my height above? Well, let me level the ground.
03:21
Yeah. Let's separate those terms first. Because you said, I said, what's altimetry? And you said something about and use the word height? Yes. So that's distinct from the word altitude. Yeah. So what is height? So height is your distance above said objects to the ground easily whereas altitude going.
03:53
You can say something when you learn the two uses of the words in aviation yeah. High is your distance above the runway and altitude is your distance above sea level. Yeah, your flight level is your distance above a datum, 1013hpa, here. So say we should make sure we use the word height and altitude.
04:17
Which I hear people use the word high incorrectly all the time. And since I haven't done any general aviation for a long time, I've not set the QFE no, for a very long time. No me neither. I used to love it. They because when you touch down it reads zero at the threshold.
04:33
back to topPressure Altimetry
Yeah. And when I was in the circuit I just flew out a thousand feet, I didn't have to fly it. Yeah, 1270 feet. Exactly. So I missed the QFE. So let's talk about barometric altimeters on our aircraft on the, on the airbus. So what have we got in the flight deck barometrically?
04:52
Well, I've got a PFD. Yeah, my colleagues got a separate, PFD primary, flight display, yep. With this most amazing altimeter, which I take for granted. The display is what I'm referring to, yeah. Because the three-pointer style altimeter, the drum barrel style and so on have been attributed to accidents by pilots misreading, miss reading them.
05:19
Yeah. Various and so they like to use combinations of those but the one that we look at is so clear. Yeah. And the way they've integrated, which will come on to radio altimetry on top of. Yeah, pressure altimetry. Yeah, is really good. And we also have standby instruments in the flight deck, which may be an older fashioned style of display display.
05:43
But like a lot of things on the aircraft, we have three separate sources. Yes, that's important of air data. Yes, which we can kind of move around the displays, but you should have in normal situation, three, separate displays of three distinct separate air data. And if one of them is unserviceable, you could turn that one off and still have three displays, but from two sources, right?
06:12
Yep. So we like three things for redundancy and complex. Yeah, airliners okay so we're wherever Manchester Leeds Heathrow takeoff on wherever just the places we've just been with, we would would depart on the local QNH here for that airport, which would obviously. So they are reading on the altimeter would be the heights, the elevation, essentially of that airport above sea level.
06:43
So yeah, 200 feet, 250 feet, wherever 600 is 600 leads. Usually, yeah, LHR is what to 200? Just under 200. I think mean sea level, that's what they say mean. Let's sea varies in like I don't know, the tide maybe anyway. Well yeah, that's a whole, that's a whole podcasting itself if you want to fly really close to the ground.
07:06
Yeah, your best staying away from pressure, altimetry. Yeah. So you don't have to worry whether the sea is gone up or down a few, a few feet that day. But, yeah. So I've got a really good story about flying very close to the ground, which I the, you know, about, but we'll come on to that later on because that's exciting.
07:22
I hope it's not like me or you doing there and everything. Okay and so he throws a couple hundred feet leads, for example, sits on a hill leads Bradford says 600 feet. So when you're sat in your aircraft, doing your pre-flight checks and you have a look at your altimeter, it should say, and 600 feet in leeds.
07:42
Yeah, exactly. Yeah, okay. Providing you set the QNH it's correctly. So then you take off and if you had just all flying around the circuit leeds down initially climbing out on the standard instrument departure, you'd stay on that QNH until you reached the transition level which I hate the definition of transition level and transitional altitude.
08:03
Yes, it messes with my brain but luckily for me practically you don't need to really know where it is. No, when you're under radar control. No, exactly. And the idea being of that that once you've passed through that everybody sets standard pressure which is 1013 millibars. Hmm.
08:22
So that if you take enough from Heathrow on a QNH of say 1 0 0 3 and somebody's taken off from Manchester on a QNH of 1 0 0 1 and you're converging to each other eventually once you've gone through the transition level everybody's on 1013. So we've all got the exact same.
08:39
Yeah, pressure setting because when we take off from Leeds and there's the peak district around or the Yorkshire Dales, and then we want to know what our altitude or high is reference to the terrain. Yeah. Yeah. But once we're away from the terrain so they'll set the transition level.
08:58
Well above any terrain for that country? Yeah. Because I think in the states is like 10,000, maybe yeah. Yeah. Some places are really high. The UK is different to be a six usually between six and seven thousand feet normally. So once we're above well above terrain, it doesn't really matter how close to the train.
09:16
We are as accurately as it matters. How close we are to other craft. Exactly. We need to know what our altitude is with reference to their aircraft and like you're saying if there's high pressure down in London and slightly lower pressure up, north it leads, then as you travel from one place to the other, you're going to be on different QNHs , exactly.
09:35
It's just not going to work. So you all need to be on the same pressure setting. Yeah. So that so that we're all nice and separated. Yes. From each other. Not from the terrain. No from each other. Exactly. And we usually use a thousand foot separation and this is it.
09:52
It's kind of emphasises the importance of making sure that you have your QNH set, but also it also links into every as long as everybody's on the same. Then you're always going to have a thousand foot separation if somebody's unless you're altimeters not working. Correct. Yeah. That's yeah. Absolutely.
10:10
So a thousand foot separation is our RVSM? Yes which isn't been around forever. No, I think 2002 and Europe led the way of RVSM. Yeah, and be. Yeah. 2,000. Yeah. 2,000 feet was separation version and it's doubled amount of aircraft. You can fit in a box of airspace essentially.
10:32
Yeah so they eventually did it over the Atlantic as well so again went from 2000 foot separation to 1,000 foot separation and I learnt that something I didn't know which is that during the implementation of that. They, they being the regulatory bodies, wanted to know how accurate, actually, everybody was keeping their altitude, right?
10:55
Because now are only a thousand foot separation. So they wanted some kind of check on it, right? So did you know that they actually geometrically measure our altitude in Europe in that busy busy part of airspace with something called height measuring units. Okay. So they get the ping off the transponder like how GPS works using the time.
11:21
It takes to ping that aircraft to a certain station and another station on another station. I think they except they triangulate it. So they work out your geometric altitude. Nothing to do with your pressure reading, nothing at all, and they compare it to what you're supposed to be flying, right?
11:38
And they actually hone in on certain airframes that have bad altitude, keeping? Okay. And then they all contact the company and say, you know, G-BBBA. Yeah, is always flying 200 feet low, okay, that's interesting. And they can also track certain manufacturers or so aircraft types and say that aircraft.
12:00
They're not keeping initially or not. And they're always 100 feet low and you can see these graphs of where they've intervened and then the altitude keeping's got better. So vertical separation is so important to safety that they needed to introduce RVSM. But they were so worried about altitude, keeping that they, I'd ever realised that they actually monitor our geometric altitude to see if your aircraft, your company, your manufacturer has good alternatory.
12:34
That's really interesting. I didn't know that. I'd not really bother. Yeah, I didn't know that, you know, we could go on just loads. So you could talk about the they downsides of thousand foot separation. In terms of how busy and TCAS or did you look into überlingen air crash for this?
12:54
I didn't but I know. Yeah, I I was tempted to but I didn't either. So I have to look at that another time but that is that maybe that's another podcast. Yeah, I think so. Yeah, be a good one. So TCAS is a system that helps us keep vertical separation when things have gone wrong.
13:10
Basically? That's the same busy piece of airspace that where they first introduce RVSM. Yeah. But I just like exploring the idea of like, what you say, basically you're out. Altimeter is not really an altimeter. Yeah. Yeah. It's just a, it's just a barometer like your granddad might have on the wall.
13:30
Yeah, house. Yeah, haven't you got one, yeah I have. I have got a barometer well then and then basically it's just someone's painted over the barometer with without you. It's a lie. It's a lie. Yeah. But everyone's telling the same lies. Why at the same time?
13:44
Yeah. So that's fine. So it's really a pressure measuring device that we can use to approximate our altitude. And I think, the more you appreciate that will perhaps, try and store that away. The more you will just always have in the back of mind that there's a limitation to this device.
13:58
That is so crucial to the operation. And, and not put all your faith into it, because obviously, there's accidents, where incorrect, pressure settings, or problems with the, the system and failures, of course, like big loss of life. And I just like also you know, understanding that the pressure is higher sea level and the pressure.
14:22
Reduces you go up for one simple reason gravity. So obviously the effect of gravity is stronger towards the earth so the air is denser and as you get higher and higher and higher, the air gets less and less dense. And so I just I just like the simplicity of that, but the relationship of pressure with height is not linear and temperature it is but that but we rely on the temperature might not be.
14:51
There's all these problems with our altimeter but we get it to work through all sorts of international standard atmosphere and then these super, super accurate altimeters which are just measuring pressure. Like, see practically. So I just thought. So I'm like if you go from A to B on one zero, one three and you're going from high to low, then to high pressure again, you're actually riding the 1013
15:13
Like isobar almost. Yeah. And we're all doing it. So, it's fine. Yeah, you're actually going up and down. Yeah. You just have no idea because when I'm sat in the cruise, and I want to feel like I'm sat on the top of like a tower, that's labelled, FL350 and then my aircraft dips, or the speed, like just very slightly and I get annoyed with it.
15:34
Like, what's this doing? Little do I know, you know, like I always say we try and operate the aircraft so precisely to the nearest foot, you know. It's the nearest kilo of fuel flight to the nearest knot of airspeed, but the environment that we operate in is so imprecise.
15:49
And this is like the best example of it. But because what is out, what is altitude is? Yeah, it's a lie. It's a lie because we just use this standards kind of 30 feet per hectopascal. For example, you, you're talking about your your wave of 1013 if you took off somewhere, pressure, setting of 1030 and flew not very far.
16:12
Maybe a couple of hours to someone that was like, 1 0 0, so 30, millibars different. Yeah, you actually will be like a thousand feet lower. Yeah, the time you get there but you wouldn't know that because you asked me to still read the same. Now it's a massive fudge.
16:28
And then when you think about you think, well hi what's the what do they call the earth is oblate? Spheroid with the geodetic mean, so the ground is growing up and down. Anyway, yeah, as much but at least everybody's just doing the same thing. So hopefully hopefully with these super super accurate and then this is the problem, isn't it?
16:46
Like the air is there's a lot more volume to the air than the ground. We're light used to be in these 2d people really who live on this one plane and it's like, I so crowded down here. Yeah. But then, you know, like a skyscraper of apartment shows you how much more space there is when you go up?
17:04
Yeah. Right. That's why like, you know, when it's 5pm and everyone leaves the offices and then they're all stuck in traffic because they all live in high. They'll work in high-rise officers and then there's only one plane for them to drive on. Yeah, right. But in the air, there's loads of planes because there's well a thousand feet every time fee.
17:22
Yeah. But the problem I'm saying is we all fly so precisely and laterally on navigational tracks, that sometimes you can go ahead to head of an aircraft. Yeah, which is ridiculous. Yeah, so like we offset our lateral tracks sometimes just to introduce a bit of randomness but we don't offset vertically.
17:39
Probably for good reasons. But you know when I was doing GA I used to fly around like at 3,000 feet exactly or something. So everybody I should have just like, yeah, shit. I just feel like maybe was I doing the wrong thing, you know. introduces some randomness. Yeah.
17:53
It's everyone's at 3,000 feet is true. That's true. And and then perhaps before we move away that just the the idea that yeah, when you, you're basically measuring the out, another way to think of me is you're just measuring the weight of the column of air above your aircraft and so if if it's warmer or cooler, that affects the density of that, that thing that that you're measuring.
18:16
So yeah altitude is BS, but it's super important. So we've established it. What's your favourite pressure setting? I've never really thought about that ,1013 probably. Yeah, and when I'm doing like simulators running simulators, it's just easier to just do one two or one.
18:35
Three serious. Yeah, that's not realistic. Okay, sorry. Well, I was gonna say, so, it all works as long as everybody's doing the right thing and we fly around on standard once or one three to get to where we're going. And then we start descending to to land somewhere and this is the more dangerous way coming down.
18:54
Yeah going you know doing your altimeter check is you mentioned on the ground that he threw at the start of the day is fairly straightforward because you're on the ground. You checking the elevation and you take it off up into the air? Yeah. Well there's nothing. You're gonna hit coming down towards the terrain and the ground.
19:08
That's where problems are going to arise and going back through the transition level onto local QNH. You have to change your alternator setting. Now this is where this is where problems can occur. For example, with like language barriers, etc. So you often hear this set QNH is mm-hmm.
19:29
So if you heard, if the QNH was say 1013, when you heard 1033, that's 30 big problem. Yeah, that's already said what? 30? Well, yes, goals is a thousand feet, so known as a problem for the ground, that's pretty bad. It's also a problem for other aircrafts because they, that was obvious.
19:52
Yeah. Well, like the different, you know, like a few hundred feet might be easy to miss. Yes, that's true. That's true. And that could create and, you know, maybe we'll talk about this, but on a non-precision approach. Yeah, that could kill you. Well, yeah, exact on an non precision approach.
20:08
The QNH is the only thing that you're flying on with reference to the ground. Really? I was thinking because sometimes do you ever think about? Like the end of the world situation and somehow you've got your hands on an aircraft and you're gonna go and fly your family somewhere. Alright?
20:21
Right. So you've got no air traffic control. Yeah. So you can set the QNH yourself on the ground. Yeah. Because do you know the elevation the airport? Yeah but if there was never any radio communication with the ground and you were flying somewhere different and you had no met information.
20:35
Yeah. How could you ever know what the local pressure was? You have no datum, you wouldn't to come into land because if you are flying to a remote airfield, like in general aviation, you kind of set the regional QNH, or sometimes they'll say, you get it from this airport and then you adjust it to this local airport or you?
20:56
Just there's a there's a certain tolerance or something. Yeah, if you had no met information at all, you would never know what the local QNH is. You just have to head towards the ground. Yeah, as the impossible, basically? Yeah, although I'm starting to think about other source that we've got on our modern aircraft.
21:13
back to topRadio Altimeters
So, the radio altimeters. So, maybe this good times to talk. Yeah, about that. So, so when, when might, you know, you've missed at the QNH then, well, so when you're already out to me, it goes off. So radio, altimeters are more accurate way of measuring your altitude.
21:31
Well, your height above the ground? And it's basically like a well, it's just a radio signal. Yeah, bounces off the ground bounces back to the aircraft and calculates your height in feet above the ground. That is directly below the aircraft. Yeah. So and it's important, if you're stupid like me, you might think it's called radar altimeter, but it's radio and it doesn't use.
21:56
So I think for example, like, combat aircraft would have like ground following radar to fly into enemy territory. So it's totally different to that and it's only it's just a simple radio. Yes, signal suit super high frequency signal between. It's about 4,000 megahertz, yep. And it's like some kind of weird frequency modulated thing and basically they bounce it off the ground and the difference.
22:21
It's essentially the time that they're measuring yet to your height above the ground. It's a slightly different and we got two of those anyway. Yeah, not just one. Yeah. See two those and that's a good point. Why don't we just gun then cross check? You know, you could cross check your yeah.
22:37
That's that might so where you would trap that you buy a miss set the QNA. If your radio altimeter is reading two and a half thousand feet and you're expecting your barometric to be the same. And it's not, that could be a catch, but we can't just to make the distinction.
22:51
We can't use that in the well, we don't use it anywhere above two and a half thousand feet. No. And I think due to the design of the instrument you can't. No because it'll be too much error. I believe you can't use it in the masking now why don't you just use that?
23:05
Yeah, but again like I said it's not relevant in the opacity because you want everyone to be on the same data. Exactly. You don't want to be some guy over one. Town is you feet higher than yeah. And if you see what it literally measures the ground right beneath you.
23:19
So exactly. So, you know, relevant so it's not relevant. There might be a massive hill underneath you. Yeah, you might actually be 5,000 feet above the aerodrome that you're landing at. But only two and a half thousand feet above the hill. That's directly below. You. Tell anyone else.
23:31
It goes off. He's flying across the Atlantic. Yeah. It's black at night. Yeah. There's nothing below you. Yeah. And it suddenly goes. “500” wouldnt is say “1,000”. Okay. Yeah. There you go. But a thousand. Yeah. Why is it done that obviously? There's an aircraft has passed directly below you.
23:50
Yeah, at a thousand. Exactly. A thousand feet below. You and obviously the audio J following it as well. Yeah, it can stay you radios right over. It has picked up the aircraft, believe you and thinks it's the ground. Yeah. Yeah. The use for thousand because it's on all the time.
24:04
Yeah and when the wheels when you when you have to've lifted off and so if you ever get intercepted by like a secret fighter jet or UFO, you would know about it. If you underneath you. Yeah. There's you can't turn that system off. So that's very accurate. And that is true if you like compared to this lie of barometric.
24:24
That is literally telling you to the foot. How high you are here above the ground. Yeah, and like you say, it's at that moment. So yeah, talking about the North England. Again, if you're on a kind of like bass leg for RWY23 Manchester, it'll go off. And when you're over there Peak District there.
24:45
So it's a trigger for most SOPs. I think when that goes off, you'd be a fol to ignore it. Yes. So what kind of what do we do when it goes off. So we've verify we you know, in terms of our situational awareness. We love hopefully pre-briefed where we expect it to go off, right?
25:05
And that will verify whether our position is correct whether we've got the QNH set correctly, did it go off where we expected it to go off? Has it gone off earlier than we expected? Does that mean? We're not where we thought? We are etc. Etc. It can help. I think I had it go off in a hail storm once actually but it's pretty good apart apart from very very rarely.
25:25
And yeah. So we we check our essay and including the pressure data. Yeah, at that point. Yeah we also use it for our stability as well for our stable call. Don't we? Oh yeah most airlines use similar but maybe yeah. Actually the thousand foot radio call 500 radio calls more infallible and yeah, not ignore the verbal.
25:49
You can't ignore the save The radio. The read radio, altimeter has a display on the PFD. That's how we know it. And it also has this beautiful like, the actual horizon, the the brown horizon starts to come up to rise. This is such a good display and even a red tape comes up.
26:07
Yeah. As you get close to the ground, but also and the manufacturer and the airline chooses certain callouts of, which there should be one at 2,500 1,000 feet, 500 feet your decision height. So you can use the radar to to ping to ping those off, which I think is what you're saying, which is, which is good.
26:30
So we use it for a thousand for another thing. It's good for is measuring the rate of change. Yep. So what system does it feed? That might be the last thing that could save your life in terms of controlled flight into terrain feast their GPWS, right? Exactly, yeah. Same warning system.
26:49
So all those like, you know, too, low, terrain warnings, terrain, pull up, those kind of things. It's the rate of change as well. Yeah. So it can't necessarily look. Well, it can't look ahead of the aircraft, although, we now have aircraft with a database over the map in, which helps the enhance.
27:04
But also, if the ground is approaching, yeah, then it then it doesn't, it doesn't like it. And but it builds a basin around there, an airport to allow you to, to get close to the terrain without spooking it. So now and then it's, I don't know if it came in at the same time, but it's really crucial for one of our automatic systems for auto land.
27:25
Yes. Yeah. So we wouldn't be able to auto land without the radar altimeter, radio alternator. I see. This is the problem. I feel like I want to say that. So to be clear it's the radio. So yeah. So that's how the aircraft manages to do. What we normally do that eyeballs.
27:43
Yeah. Which is flare and which it does a really good job of really good. And it's the height of the landing gear above the ground. It's calibrated for. Yeah, I think that's why occasionally on the ground. It reads minus because then the landing is compressed, it's slightly compressed. Yeah, yeah, minus one.
28:00
I minus two. Yeah. Yeah. Don't come and see that. Okay, so you sort of touched on something else there, which we could talk about. So you mentioned, an auto land, we use the radio alternator. Yeah, auto land would typically be often ILS approach and instrument landing system. Yes, essentially flying a beam, both lately and yeah, vertically.
28:22
All like across hairs all the way into the airport. If you haven't got an ILS approach which a lot of airports don't have then you are flying. What we call a non-precision approach. Where we are managing the vertical profile ourselves and the only reference we've got to start from, is the is the QNH?
28:43
The? Yeah. So even on our approaches, although there's kind of more modern ways of flying those. They're still based on making sure that you've set the correct QNH. Yeah. Otherwise, nothing will save you. Exactly. Say, an ILS is a precision approach, and we like to fly now non-precision approaches as precision like approaches, which means that we're using, it's basically GPS.
29:12
But, you know, it could be your inertial sources to navigate an area navigation. Are you not following them down a beam? So, you know where you are, but you're not directly going in tracking inbound to something. So, it's a non-precision approach using area and navigation, which can be very, very accurate.
29:31
However, vertically, there is no element to it. So, you have to have the right pressure set in all your screwed. Yeah, GPS altitudes available, but it's not part of the approach whatsoever. No. So that's interesting say just to be clear for anybody out there that ILS is you could haven't, you could do it without altimetres, if you could lock onto that beam.
29:54
Yeah, there's a vertical beam and there's a lateral beam and that'll take you down to the threshold of the runway as well. So you all the way in, but on approach, you need to know that this distance from the runway. I need this pressure altitude. Yeah, yeah, exactly. So GPS altitude is not used by us at all, apart from in, sort of back door, play redundancy.
30:20
back to topAeroperú Flight 603
Yeah, failure of the air data interesting that it's not, we might, we might cross reference it. Yeah, so lots of lots of potential. It's it's leading me towards a couple of accidents that I've looked into. Yeah. Okay. A couple of things that you've said. Yeah go okay well Aero Peru, okay what happened there?
30:42
Then I haven't looked at Aero Peru but I feel like I know the accident you'll know it. So unfortunately arrow Peru 1996 B757 the aircraft had been. Oh yeah on the ground and they covered the static ports with they call it like masking tape, some kind of tape. Right.
31:02
Wasn't picked up by the engineers, wasn't picked up by the Captain on the walk around took off and all hell break loose in terms of aural warnings and stuff because they essentially got ground level air trapped in the static port because it had been taped over. Yeah exactly. And so let's think that through.
31:24
So, would that affect their takeoff roll? No. No. Because the airspeed would come from the pitot. Yeah, but it's minus the static. Yeah. But say, wouldn't be affected until you climbed until you climbed when you when the static should decrease. Yeah, because we do cross checks on the air data on takeoff, which could prompt to rejected takeoff.
31:47
Yeah. So they got airborne and some pretty crazy stuff happened. It's really, it's amazing that they didn't crash for so long. I don't know what the duration of the flight was, but it makes for a really upsetting sort of series of events. Because this the situation awareness in the flight deck, sort of breaks down and down and down.
32:09
However, the first officer seems to have kind of a grasp of what might be the problem, but can't really convinced it's not that he's advocating it but it seems like he has more of a chance of doing the right thing. The couch in total loss of SA and I wanted to kind of work out if they had memory drills for unreliable airspeed.
32:31
At this point on the B757, which you assume they have all they are not. I wish I'd got to the bottom of that, but I haven't but they are aware that they have contradicting information. Yeah. Because the aircraft is they say over the radio all the time, the aircrafts accelerate in even though there are idle power.
32:53
And basically, they're stuck at 9,700 feet on the altimetres, right? And a lot of the time the GPWS system is aurally. Warning them. So unfortunately at some point they ask air traffic control. What their altitude is right? And the air traffic. Controller tells them, it's 9,700 feet and they accept that as a valid or one of the sources.
33:23
So it adds up to really break down their SA. But Sam, where's the air? Traffic controller. Getting the information. Well yeah from exactly the same source as they often that transponder. Yes. So the information that the air traffic controls got is erroneous, so just to be clear that thing that I mentioned earlier, height monitoring unit is so obscure we don't even know about it.
33:42
There's no real-time data for the out for the radar controllers on the ground to measure your altitude, geometrically or anything like that. There's nothing like that available. The pressure altitude that you have in the flight deck is transmitted via data. To the control on the ground. So if you don't know your altitude, they don't know on the ground.
34:03
So if you're in an unreliable speed situation, you tell them or possibly turn off the mode C of your transponder if the controller doesn't stand that. So in this accident, unfortunately, the amount of alarms in the flight deck was horrible. They also had like, you know, EICAS for like rudder and mack problems that were due to this and this chain of events, but it was just adding to alarms alarms alarms.
34:28
So we don't know what their altitude was doing, but we know that the GPWS was doing, it was saying the right thing. So a lot of the time they're very low but we know their lateral track and the captain does kind of have a good idea. He's like, well, if I can get on the ILS then I can land.
34:49
Yeah, but at no point. Do they do the Unreliable speed drill. So and I've said this before but basically the captain had like 20,000 hours. FO first I've said like 8,000 hours staring at altimetres that were working correctly right now. They're not, but they weren't able to blank them.
35:08
No, you know, sometimes it'd be nice to have a sheet of paper and just put it above across the altimeter, or the airspeed. Yeah. Because otherwise, your eyes are gonna get drawn into it. Yeah. So I just so, your brain is saying, look there look, I've run this in the simulator occasionally just to show people where you get an unreliable static because we always do unreliable air speed right?
35:29
I've showed them a block, static pool. Yeah. And it's amazing that you can feel the aircraft climbing, right. And the pitch is climb pitch. Yeah. But the altimeter is just staying for. Yeah and not moving horrible. It doesn't feel right because we spent so many thousands of hours looking at it and it just isn't, right?
35:47
It's just not. So, that was so powerful for these guys that they disregarded the GPWS warnings, right? They believed, what the air traffic controller was telling them, but yeah. It just stayed the same altitude, the whole time. The display. Yeah. And then in the way it ends is horrible because they, they think they're sort of, they kind of trying to troubleshoot it.
36:07
There's not too much structures to it, but the wing clips the sea and they're like, then they they realise. Oh, we've just hit the sea. Yeah. But then they have another 20 seconds, maybe of of trying to climb out right. But I don't know what damages occurred, but they're still flying and in a even though they've actually hit a bit of the sea.
36:28
Yeah, it's crazy. And then eventually they get sort of go inverted and go into the sea, at this point, the FOs, trying to sort of advocate, a little bit that the GPWS is probably reliable is almost getting there. So, the things that we've talked about already, they're relevant, are that your instruments are fallible?
36:46
And you need to understand their limitations? Yes, that the ILS doesn't use any barometric data. So, apart from you need to find your way on to it. So how and something else? I think we picked up on was relevant to this accident as well. Of course, now we'd have GPS altitude data, we could kind of cross check that.
37:05
Well, that's bullshit altitude. And yeah, also just that the radar ultimate is totally different system. So if that's going off, you know, and we have specific training on this. It's not as ambiguous as I'm about to make out to be. But some, you know, what do you believe? Do you believe the stall warning
37:22
Do you believe you're a airspeed tape? Do you believe the GPWS system? Do you believe your pressure altitude? So you need to be aware a little bit of the technical aspects of these systems. Think which one? Which one is likely to be reliable? And what's the chance that they're both wrong?
37:38
That's how. Can my GPWS? And my barometric altitude. Both have failed today, but so many alarms in the flight there definitely wasn't helpful. I am say, that was one. And then unfortunately, another B757 took off in the Caribbean and an insect had decided to move into the static port.
37:58
I is, it's Birgenair and it is a charter flight and it and that had blocked the static port, right? And that accident is, my memory is failing me now but it was different but was blocked. Static port on our 757, not to not too long after so that's a shame but what I wanted to find out which I didn't find out.
38:23
Was now I feel like we've got very rigid drill for like if there's any ambiguity here? Yeah. About the air data. Yeah. Then we go into a memory drill. Yep. We it's a look it up or anything like that and we go back to basics if you like, which is pitch and power to power and we can fly the aircraft safely on pitch and power.
38:43
Yeah. And to a point where we can troubleshoot, but until that point, we don't look at one of the three and go. That's the right one. That's the right. Yeah. Because we don't know at that point, right? But it seems like and these accidents that that wasn't as explicit as like, okay you go into the memory journal so they're the accidents that I'd looked at specifically with regard to altimetry.
39:06
back to topDambusters
Yes. So I I didn't look at an accident. I looked at something kind of more anecdotal and something I found really interesting and you talked about it, flying low earlier was the was the Dambusters, you know, you know that I love this. But and for any of you that don't know, sort of the detail about the Dambusters and I've only heard about it.
39:30
I'd strongly urge you to watch, there's multiple documentaries on it, but the one I watched was with Dan Snow the presenter, really, really interesting. But essentially, so when they were creating the bouncing bomb to try and destroy these dams in Germany, so much, testing went on as to what the perfect altitude or height was to drop the bomb to let it bounce along the reservoir and hit the down bear in mind in the, you know, 1940s the best altimeter out.
40:08
There was an old three dial barometric. Which, you know, would only really accurately measure to 100 feet. So it wasn't really, very well calibrated, but like I said, earlier, you can't ask the Germans for the QNH. No, exactly. Yeah. And yeah. Exactly. You can't ask me. Yeah. Just as you come into, German airspace.
40:27
Yeah. Anyway, so you say this, so what they found was that 60 feet above the water, was the perfect height to drop the bouncing bomb. So the question was, how do you fly at 60 feet at night without knowing what the QNH is from the Germans? So they came up with this really clever system, which was basically two torch lights mounted to the front of the, of the Lancasters.
40:57
And essentially, they were calibrated to such an angle that as the aircraft came over the reservoir at night time. Obviously generally, perfectly flat level plain the, the reservoir, these two torch beams move closer together and when they made a perfect figure of eight on the water light on the water, that was exactly 60 feet.
41:19
And I just thought that was such a nice anecdotal story of like, altitude and altimetry like 60 feet. These guys were flying out and literally just as simple as two torch lights. Yeah, could fly. So accurately. Right, what works? So clever ingenious way and then they would obviously drop then.
41:37
I drop the bouncing bombs from from that 60 feet. Say, I just thought I'd share that as a as a sort of little side story on altimeter, I like it because well there was a point in terms of navigation where we did it all by using ground-based system.
41:53
So you'd fly in towards the beacon and then turn away in the way you want to go outbound on a beacon? Yeah. And then we started using area navigation which we still use ground-based stuff. Now, we're moving to a world where it's stuff on the aircraft, you know, so you you're making on-ever approaches using GPS.
42:11
Yes. But then the GPS isn't actually on the aircraft. Everybody thinks that I'll never go down, which probably won't because there's multiple systems now, but it has caused accidents in the past and people have been shot down because of their navigation error. So in the same way, in terms of altimetry, it's like what can we have on board.
42:29
We got this wicked radio altimeter now which is but wonder if other on board stuff like the GPS will become yeah. Relevant you know, in the upper atmosphere or yeah. Possibly. But there's guys in the Dambusters they have to have everything. They're not gonna get any help from the ground.
42:47
Yeah. Yeah. Every system had to be on on board system. Yeah, you're not gonna have an ILS into your target site that bomb. Yeah. Everything had to be on board including the altimetry. So two, light bulbs, two light, bulb one, just had spare light, but what if the filament went?
43:02
Yeah. Exactly. I don't know. Yeah, I mean interesting, yeah, it was such a simple piece of technology but worked perfectly, you did your brain, you listen to the radio radio ultimate call outs when you flare not consciously. No. You think you don't do it on that or well. I I don't know, maybe I do more now as a training captain because they teach that that's how we teach it for.
43:26
People learning to learn the airbus and maybe I'm more conscious of it. Now it, what about like the texture of the ground? Or, you know, do you actually have a little of you have how low you are? Yeah, I think it's more on judgement now by just looking out the window and judging it was supposed to look at the end of the runway.
43:42
It's not that I'm saying. So yeah, exactly. Whereas I think in your early days, you probably did use the radio altimeter, more as your gauge to help you flare and land. Yeah, yeah. Well hope we've destroyed the concept of how to meet us. So next time passenger says, you know or you make your PA how high we are but I wouldn't suggest you tell the passengers.
44:02
We don't really know just so just guesswork. But we're all doing anything. Yeah exactly. Don't worry about it and yeah. I think we've then we've talked about some interesting, interesting, sides to our altimetry there. So yeah. Thanks very much, bye.
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