The very short version is the ATC controller messed up one digit of the altimeter setting and the pilots entered what the controller said into their altimeters. Not noticing that setting differed a bunch from the last ATIS. Unsettled weather was a factor and the difference, though large, wasn’t outrageously large.
But it was enough (~300 feet), that they damn near impacted the ground a mile short of the runway.
An ill-appreciated feature of modern GPS approaches is that, unlike ILS, they do not have true geometric guidance in the vertical dimension. What they have is a projected vertical path that depends on the correct barometric altimeter setting to anchor the start and end points of the final approach segment in 3-D space. If the altimeter setting is wrong, you’ll fly exactly parallel to the correct vertical path, just displaced upwards or downwards by however much the altimeter is misset.
If displaced upwards, you may never break out of the clouds and if you do break out of the clouds you’ll be higher than expected for that point along the lateral track to the runway, leading to a temptation to dive for the runway. Which has caused more than one accident.
If displaced downwards, you’ll be closer to the terrain at every point on the approach. Which might have you intersect an intervening hill or antenna or smokestack during descent. If there are no obstacles but the weather is low, you’ll come out of the bottom of the clouds some distance short of the runway. Maybe you’ll be ready for that aggressive go-around and maybe you won’t be. Or you may decide those roadway lights just ahead must be the runway so you attempt to land on them. Oops.
Or maybe, like these folks, you never break out and commence the go-around at the correct indicated altitude, but commence it a bit late and / or a bit lazily and come within a hair’s breadth of striking terrain. Yikes!
I’m not certain that’s correct for all forms of GPS approaches. Last I recall from training, fully WAAS-enabled LPV approaches are geometrically generated and don’t depend on barometric data. But what you described would be true for LNAV / VNAV, which does require pressure data.
Not sure what’s prevailing in the airline world. In my bizjet universe I’ve done a lot of LPV approaches and they’re great. I like that they don’t depend on any ground stations (apart from what’s inherent to the WAAS system), and aren’t subject to certain types of interference that could affect an ILS.
It’s interesting - LPV has been around for a while now. I first encountered it when I was an instructor probably around 2004, shortly after WAAS was certified for use. At that time there were a lot of refurbished Garmin 430s becoming available and suddenly every Cessna and Piper in the world seemed to have one installed, yet nobody really knew how to use them. I read a lot of manuals and ended up doing a good business semi-specializing in GPS instruction.
But it was difficult because there were so many new features that could be confusing. In particular, there was “LNAV+V” - under certain circumstances, while flying a non-LPV approach you would still get a glidepath. The Garmin manual had exactly one sentence to say about it, describing it as “advisory” with no further information. I had to make a lot of phone calls to find out the details of that feature and how to properly use it.
All this to say, the airlines are smart to be careful and conservative about integrating new procedures. I’ve run into confusion more than once in bizjets with GPS approaches, and I was dearly grateful for my past experience while trying to dope out what the avionics were doing. And once when I flew for a regional I had a captain try to do an approach using a certified, but ancient GPS unit. It went bad, but with great luck I actually identified the problem based on what I had seen while instructing years earlier (he had mistakenly triggered OBS mode, which is mostly used for holds. I recognized it because it’s one of the few times you’ll see a GPS distance counting up rather than down). The devil really is in the details.
I’ve been glad to have LPV available to me in the charter business, going into many airports without an ILS. But the airlines have the luxury of usually having an ILS available, which means there’s let impetus to adopt LPV (and not incidentally, absorbing the costs associated with installing the necessary receivers and antennae).
Which isn’t a new problem. An incorrectly set altimeter will cause the same issue on an NDB or VOR approach. My employer requires us to receive the current QNH from ATC once below transition and prior to the final approach fix when flying a non-precision approach. We are also supposed to avoid priming ATC with the value we have, so if we have to ask for it we would say “confirm QNH” rather than “confirm QNH 1006”. By contrast in my previous life flying in Australia no one seemed to put much emphasis on the QNH, it was assumed that if you have the current ATIS then you have the correct QNH and you would be given the QNH when cleared to an altitude on descent. Current employer is sometimes mocked by Australians for our over emphasis on reading the QNH with the ATIS and at any other opportunity we get.
We have GLS approach capability in the A320. It uses GBAS to achieve accuracy similar to ILS, and like @Llama_Llogophile says for LPV, it is excellent for behaving just like an ILS without having any of the cons of an ILS such as false captures, side lobes, ground interference, etc.
I don’t think GLS counts as an LPV approach though, instead it is a genuine precision approach. We don’t have LPV in this part of the world and GLS are only at a couple of major airports in Australia with none in New Zealand. Mostly it’s either ILS or RNP.
Side note that the naming conventions for RNAV/GPS/RNP approaches are still a complete mess despite ICAO doing their best to tidy it up. I was picked up by ATC yesterday for reading back that we were cleared for the RNAV approach runway zero five when we had been cleared the RNP (AR) approach. The reason I had said “RNAV” is that when I read back the clearance I like to confirm it matches what is displayed on the nav display and the A320 nav display still shows an RNP approach as “RNAV”, so I had just read what I was looking at.
Quite right. Lotta people have died that way over the years. What seems to be unexpected by many pilots and indeed some flight department managements is that in baro VNAV that nice purple line and stable computed vertical path stuff isn’t coming from the 3D GPS position. It’s 2D GPS + altimeter.
That policy should apply to any/everything by everyone everywhere. If you have a question, ask them to deliver all the info afresh. Don’t tell them your (possible mis-) understanding and ask them to confirm. That’s setting a trap for them to fall into.
Yep. And FAA went their own way at the outset and have belatedly agreed they screwed it up completely, but can’t quite bring themselves to simply do it ICAO way. So they’re transitioning to a new and different FAA-specific nomenclature with a different set of incompatibilities and traps vs ICAO terminology versus old FAA way. At least it’s expected to take at least 10 years to rename everything, so now we get to deal with new ICAO, old ICAO, new FAA and old FAA naming. Gaah! At least our company came up with one standard to rule them all that’s different from everyone. So we say one thing cross-cockpit and something else on the radio.
Oh yeah, as you say, the different brands of aircraft avionics display their own idiosyncratic names for these things too.
2008ish; smart phone are new but most people, including me, don’t have one yet.
It’s time for the annual bike-balloon race. I know where I’ll be finishing (back at the field) but not where I’ll be starting from (wherever the balloon lands) so I can’t exactly plot my course in advance. As most of you know, things look different from the air than from the ground (ie. looking at a roof of a building vs. the siding) so I can’t even go downwind & ride around to reconnoiter. However, I do find a handlebar mount for my Garmin Nuvi. Perfect! I’ll put in the finish line address & it’ll just dynamically route me there. We’re flying along & cross over some intersection at 800’ & it’s telling me to, “Turn left”. Look down; Ummm, I don’t think so!
I owned a Garmin eTrex, which had elevation in it, & we had whatever model Garmin in the balloon which also gave us elevation but the Nuvi series was for vehicle navigation & vehicles should always be on the ground so until I had one in the air it never even occurred to me that they would program that out of that model.
Yeay, Biden is out!
Why am I posting this in the Aviation thread? Because after 4 years of Trump summering in Bedminster & almost 4 years of Biden in Wilmington it’s time for some other area to deal with not flying at all on the weekends because of all of the @#$%& TFRs. C’mon, anyone but Trump (or Josh Shapiro)!!!
Just my largely uninformed opinion, but I think we go way overboard with VIP security in aviation. I vaguely remember reading about how other countries do it, and it turns out nobody else shuts down significant parts of their national airspace every time the president or prime minister sets foot in public. Or… you know, LIVES somewhere other than their White House equivalent.
As a pilot, I’ve flown many VIPs and I’ve dealt with presidential level security a couple of times. I just can’t see how the hassle to everyone is justified. It seems a huge waste given that many of the threats from aviation appear mostly hypothetical, but I’ll certainly admit I’m no security expert.
Southwest has gotten a fair amount of criticism in this thread over the years. But the big news lately is that it missed being affected by the Crowdstrike outage. And the reason is that it is using the technological highly advanced:
Could this be because most Australian airports don’t have high terrain nearby, and many NZ ones do? If that’s even true, just a guess. But if you’re used to flying into airports with no mountains within 100 miles, I can understand not being too worried about 50’ of altitude.
Sorry for the double post, but over the weekend the UK’s AAIB released their report into a February 2023 incident involving a B767 (AAIB investigation to Boeing 767-332(ER), N197DN - GOV.UK). It suffered a contained engine failure on takeoff and although the engine was still producing thrust, the crew (on a flight from Edinburgh, UK to New York) decided to make an overweight landing at Prestwick. All went fairly smoothly, with no injuries, but fuel was pouring out of the wing because the vibrations from the engine failure fractured a (water) drain tube that passed through the fuel tank. Some of this ignited in the exhaust during the flight (captured on video by a passenger) but luckily did not escalate into a catastrophic fire either in the air or on landing.
The report isn’t critical of the flight crew as such but I think, reading between the lines, they might have done some things a bit better. In particular, the pilots weren’t aware of the flames during the flight, though in the end it didn’t affect the outcome.
The report also says Boeing has investigated, and determined that a fracture of a drain tube is not likely to increase the risk of a catastrophic outcome. But based on this report, I’m sceptical - it looks to me like this could very easily have become catastrophic. I think the AAIB agrees, as they’ve made a safety recommendation to the FAA to review the safety of this part of the design. It will be interesting to see what comes of that, with everything else going on.
Layperson’s question: why can’t the drain tube be made of a flexible material, precluding the possibility of fracture in the event of fatigue or excessive vibration? Is it largely because even if such a material exists, it would need more frequent maintenance/replacement?
I haven’t read the report and don’t know the design here, but some general comments;
The classification of a “catastrophic” event is based on functional hazard/system safety assessments and probabilities based on the specific design and mitigation factors. This failure was contained and the fire did not spread and it’s possible that this was because the design did not make it possible to spread (again, I haven’t read this report). Thus, if the original safety classification was “hazardous” or even “major”, this single event where everything worked as designed won’t change that classification. The layman usage of “catastrophic” is not the one being used here.
Now, this doesn’t mean the design is great and perfect; it’s quite possible that some redesign or new procedure will come out of the aftermath of this (it may already have done: a corrective action, if one was needed, would not have waited for this report before being published and mandated).
This is an older aircraft design with an older fuel system, in the regulatory sense. It was not compliant to the latest and greatest fuel safety standards, in the same way that my 1950s home is safe, but not compliant to 2024 building codes. You can’t design to rules that don’t exist. If there’s retrofit needs, they will be identified.
As for flexible tubing, it’s possible that at the time the system was designed (could be decades ago, if it was never modified in a major way) there may not have been flexible tubing available to meet this purpose. I’m not sure there are any today (I’ve never looked into it). These types of materials might break down too quickly when immersed in fuel. Their movement/vibration might lead to buildup of static charge which is a big no-no, the mounting points and attachment fittings of flexible tubing are typically failure points which may require much more frequent regular inspection than a traditional metal tube, which isn’t acceptable for the aircraft’s mission profile.
Traditional materials like metal are affordable, predictable and suitable. They are heavier and require corrosion and fatigue management, but their behaviour is very well studied. Plastics, rubbers, flexible tubing are much more subject to environmental degradation and less predictable failures.
While the user that posted the above statement has come out and said that he was “trolling,” other X users have taken this opportunity to create memes and poke fun at the airline and its alleged attitude of “If it ain’t broke, don’t fix it.”
I’ve heard that that’s supposedly the real reason Southwest doesn’t charge for checked bags – back in the late aughts when every other airlines was adding bag fees, Southwest was running such antiquated reservations software they literally couldn’t charge for bags even if they wanted to. So their marketing people decided to call it a feature. I thought they switched over to AirTran’s ticketing system after the merger, though.
I completely accept I probably have the wrong idea about the precise meaning of “catastrophic” in this context. Nevertheless, clearly the AAIB wasn’t completely convinced by Boeing’s assurance, otherwise they wouldn’t have made the safety recommendation. No doubt the current climate around Boeing played some part too.
There are two different processes at play here: the airworthiness process and definitions and the accident investigation process and definitions.
The AAIB is not the regulator; they cannot mandate any sort of change to the airworthiness process, to the design/definition and construction of the aircraft nor to its operation. They can make recommendations but the regulatory agency (CAA UK in this case) is the only agency able to change the laws or mandate a corrective action, and they themselves can only do it as applicable to aircraft registered in the UK.
Similarly, the American NTSB can make safety recommendations but it is the FAA that is the regulator. Likewise for the TSBC vs Transport Canada.
The NTSB has been recommending to ban “lap children” for decades. No luck yet!
So, in a regulatory sense, the aircraft was seemingly compliant with regards to the airworthiness definition and procedures that applied to its design. That doesn’t mean the definition and procedures were adequate.
In fact, I’d assume Boeing likely used the older guidance on the subject (just based on the age of the plane) and we know that there’s new guidance in works (approved in Europe, still in rulemaking in USA/Canada) to update exactly those regulations because they aren’t as complete as the industry needs them to be.
ETA: the regulations and guidance surrounding the classification of components and systems as “catastrophic”.