14 ms·
Plane drops to 928 feet after autopilot set to 0 altitude
- broahmed 8y agoAir Accidents Investigation Branch (AAIB) bulletin on this incident (it's the first report on page 3). Posting mirrors first so we don't crash a little gov site if this gets popular. Low resolution mirror: https://drive.google.com/file/d/1P7czQkX_9_e7fBDYaFWG0OlwtppgLh9R/view?usp=drivesdk https://drive.google.com/file/d/1P7czQkX_9_e7fBDYaFWG0Olwtpp... High resolution mirror: https://drive.google.com/file/d/1ulgy8cGSrG7nT1_p6PmKlxTBBi_6yVLQ/view?usp=drivesdk https://drive.google.com/file/d/1ulgy8cGSrG7nT1_p6PmKlxTBBi_... Original links can be found at: https://www.gov.uk/government/publications/air-accident-monthly-bulletin-november-2018 https://www.gov.uk/government/publications/air-accident-mont...
- Symbiote 8y agogov.uk is the British government "everything" site, regularly featured here for their technical and design approach. I'm sure they'll be able to handle whatever traffic is thrown at them for a couple of PDFs. assets.publishing.service.gov.uk is an alias for www-gov-uk.map.fastly.net.
- broahmed 8y agoThanks for pointing that out. I wasn't paying close attention to the URL and thought the report was hosted by a possibly smaller UK gov site. Didn't realize it was THE main gov.uk site! If I could edit my original comment to give precedence to the original report link, I would!
- abluecloud 8y ago> a little gov site it's the main website for the UK government, not sure if mistaken or a sly little dig at the UK.
- starbeast 8y agoThat doesn't necessarily mean it isn't just an old laptop in a cupboard somewhere in Whitehall with the network cable duct taped on so that the cleaner doesn't accidentally disconnect it.
- broahmed 8y agoNo dig, just mistaken. I wasn't paying close attention to the URL and thought the report was hosted by a possibly smaller UK gov site. Didn't realize it was THE main gov.uk site! If I could edit my original comment to give precedence to the original report link, I would!
- mrunkel 8y agoThanks for posting the links.
- broahmed 8y agoYou're welcome!
- minitoar 8y agoI would think the pre take off checklist would include configuring autopilot for your planned departure altitude/heading/whatever.
- duxup 8y ago>The report said "several safety actions" had been taken by Flybe since the incident, including revisions to simulator training and amendments to the taxi checklist. I wonder if that is one of the amendments.
- mrunkel 8y agoIt does and did. They set the correct altitude. They put the autopilot in the wrong mode.
- deleted 8y ago[deleted]
- post_break 8y agoQuestion, why is 0 a valid entry for autopilot? Would that ever be used?
- AWildC182 8y agoAltitude is above sea level, and there are airports and areas below sea level. This in and of itself causes all sorts of problems from time to time whenever a programmer forgets this and encodes altitude as an unsigned.
- skykooler 8y agoNo. But the scale has to start somewhere, and 0 is a convenient number.
- mrunkel 8y agoTypically/historically, autopilot systems have very few checks and controls, mainly because pilots insist that they know better. Having worked with several autopilots in sims, they are extraordinarily user UNfriendly and unnecessarily complicated. But, aviation is extremely conservative (and rightly so) and as such, changes and improvements are very small and incremental.
- jolmg 8y agoKnowing nothing of aviation myself, I imagine it's the same reason people prefer stick shift over automatic transmission in cars, and command line over GUIs in Unix OSes. It's a matter of favouring superusers/powerusers by leaving them with maximum control of what they want the machine to do. Often times, making a system user-friendly means loss of control and ability to make the machine work its best for you.
- sehugg 8y agoIs it common to set autopilot below 5,000 feet or so? Seems kind of like setting your cruise control at 25 MPH.
- will_asouka 8y agoYes. Most approaches start from 2000-4000ft.
- mrunkel 8y agoSure, if you're coming in for a landing, you will dial your autopilot down as you are granted clearance. Ultimately you will switch to approach mode which ignores the set altitude and instead follows the radio signals down to the ground.
- sokoloff 8y agoExtremely common to use altitude pre-select for intermediate level off points on approach. At my home field, the highest such figure is 2000’ MSL and the lowest 720' MSL for an airport around 150' MSL.
- PhasmaFelis 8y agoThe article makes it sound like the autopilot was engaged, the plane slammed into a dive, and the pilots panicked for 18 seconds before finding and fixing the problem. It looks like what actually happened is the plane started to slowly pitch down; the pilots were busy with the after-takeoff checklist and didn't notice for 15 seconds until an alarm went off, when the pilot immediately disengaged the autopilot, pulled up, and reduced engine power.
- dsfyu404ed 8y agoImagine being the flight attendant trying to pour coffee in what was probably a 1.5G (or thereabouts) maneuver.
- sokoloff 8y agoThe cabin crew is almost surely seated below the 10,000’ MSL level. (Many airlines give the cabin crew a chime signal to indicate they’re in the climb, high enough, and expecting it’s safe to begin cabin service. Below 10K, cabin crew is focused on safety not coffee service.)
- VBprogrammer 8y agoIn an ideal world this might be true. In practice below 10000ft the cabin crew are focused on grabbing some lunch, a drink or just a rest before the rest of the flight. Source: My partner is ex-cabin crew.
- yashap 8y agoWell, it does say they reached a descent rate of 4,200 ft/min (72 ft/second), which is pretty rapid.
- shawabawa3 8y agoyou only feel acceleration not speed though - depends how quickly it accelerated to 22m/second - presumably linearly through the 18 seconds? which means 1.2m/s^2, or about 0.12G - not that extreme really
- hef19898 8y agoReports like that are one of the reasons why I love aerospace. Where esle do people dive that deep into highly complex systems, no matter the time needed, to find the root cause. And come up with solutions afterwards. You can learn a lot system complexity, root cause analysis, human factors and a ton of other stuff from it.
- joshstrange 8y agoThis is why I love "Mayday: Aircraft Disasters" (or whatever it's being called now). While the acting is cheesy as hell I really enjoy the "Ok, this happened, now let's figure out why and make sure it doesn't happen again". If you can get past the acting it's really a decent show.
- Symbiote 8y agoFor the railways. Other criticisms aside, Britain's are some of the safest in the world, and I think it's because of the same approach. I like that the report on the tank wagon has detailed pictures of failed welds and so on. Maybe the one about the "loss of speed restrictions" would be of interest to HN, since it seems to be a software problem and its subsequent analysis. https://www.gov.uk/government/organisations/rail-accident-investigation-branch https://www.gov.uk/government/organisations/rail-accident-in...
- kevin_thibedeau 8y agoBritain's preoccupation with preserving buffer and chain couplers is not a picture of safety.
- slededit 8y agoI cringed just watching the man between the two cars as they are put together. That is horrendous. https://www.youtube.com/watch?v=CIUiyavOpO0 https://www.youtube.com/watch?v=CIUiyavOpO0
- mrunkel 8y agoThis is entirely caused because autopilot (Flight Management) systems are complex beasts with minimal feedback and sometimes very subtle interactions. Ultimately the problem here was: ALT mode was selected accidentally ALT SEL mode was selected later, but ALT mode wasn't disengaged manually and engaging ALT SEL while in ALT mode doesn't disengage ALT mode. A combination of other factors (rushed during takeoff, interruptions from ATC, unfamiliarity with the Airport) caused the workload to be such that neither pilot picked up on the numerous subtle visual clues that showed that the autopilot was not going to do what they were expecting. Luckily, after descending 500ft in about 18 seconds, audible warnings in the cockpit alerted the crew that things were going awry and they very quickly remedied the situation.
- zaroth 8y ago> after descending 500ft in about 18 seconds The article says a maximum decent rate of 4,300 ft/min, so almost 3 times faster than that. They were about 13 seconds from crashing into the ground if that rate held constant.
- sandworm101 8y agoIt sounds far worse than it is. 13 seconds is a huge amount of time. Any pilot would react and correct in a second at most. This isnt some slight drop noticed by scanning instruments. They would have felt this and reacted by instinct. Autopilots off, throttles up, arrest the drop and regain a climb. Over and done within moments. They may have even deliberately let it fall a bit to gain speed, if they thought this might be a stall.
- LitFan 8y agoIt's not what you meant, but "moments"[0] is pretty a pretty long time in this circumstance. [0]https://en.wikipedia.org/wiki/Moment_(time) https://en.wikipedia.org/wiki/Moment_(time)
- jessaustin 8y agoPlease re-read parent. They already had not felt, reacted, or corrected in 18 seconds. If the bells had gone off later, they would have reacted later.
- OliverJones 8y agoThe system functioned as designed. The ground proximity alarm sounded and the pilot in command took control. It's possible the pilot should have refrained from engaging the autopilot during initial climbout. Pilot workload is high at that point in a flight, and fiddling with gadgets is distracting. Maybe wait until passing through 5,000 feet?
- sokoloff 8y agoMost autopilots are certified for operation over 400' AGL and that's a typical engagement level. If I'm feeling lazy or the weather or departure procedure is challenging, I'm more likely to be on AP than not. By all means, the pilot/crew needs to be monitoring things and always ready to hand-fly the airplane without automation, but proper use of automation is safety-enhancing. When the automation fails, go down in level of automation and hand-fly if needed. Good presentation on the topic from an American Airlines training session: https://www.youtube.com/watch?v=pN41LvuSz10 https://www.youtube.com/watch?v=pN41LvuSz10
- kss238 8y ago>The commander stated that to save time before pushback he had set the autopilot Flight Director (FD) modes to Go‑Around (ga), Heading (hdg) and Altitude Select (alt sel) but without first setting a selected altitude. Sounds like they were waiting on the ground and had time.
- 0xfaded 8y agoWhen I was learning to fly, one busy day my instructor and I were stuck waiting on a taxiway so he pulled up the autopilot and we had a play. One of the preflight checks is that the autopilot is disengaged for takeoff, but we did this after the checklist. We took off with the autopilot set to something like 4000ft, making it want to climb at an impossible rate of climb. As a novice pilot it took me several seconds of fighting the controls to figure out what had happened, all the while with the stall horn blaring on takeoff. Scary lesson.
- magnetic 8y agoI'm a bit surprised about this didactic method: being close to stalling on take-off doesn't seem to be a very safe way to teach a lesson. I used to fly and during my license test we did get into a stalling exercise to force the plane to stall at a few thousand feet altitude. This was meant to learn the feeling of sudden drop and how to recover. There is something both thrilling and scary about transitioning so quickly from seeing the horizon to seeing only earth right in front of you approaching at a high rate of speed. Being in near-stall conditions close to the ground seems to me like a recipe for disaster.
- stouset 8y agoI believe he means the instructor was showing him various autopilot features before takeoff. During this sequence, they engaged the autopilot. When they went to take off, they neglected to disengage the autopilot (since doing so wasn’t on the checklist).
- x0054 8y agoThis shows the necessity of reasonable defaults. Not a pilot, but somehow I think the default setting for ALT should NOT be 0.
- stouset 8y agoThey put the autopilot in the wrong mode. The mode they used uses the current altitude, not a default of zero. A good safety check here would be to not record an altitude if the plane’s airspeed is moving less than some value (or perhaps better, if AoA is above the critical limit as the wing is stalled).
- KineticLensman 8y agoTo be pedantic, the pilot, while on the ground, when setting (but before engaging) the autopilot selected a mode where the autopilot uses the current altitude (i.e. 0ft) as the target altitude. As mrunkel explains elsewhere, this never got corrected (due to crew work-load during take-off) before the plane reached the altitude where the pilot actually engaged the autopilot. The pilot almost immediately did the right thing and disengaged the autopilot, recovered. They then re-engaged the autopilot and the same problem happened again (but with less loss of altitude). Only then did they set the autopilot correctly. Similar incorrect settings had happened to three prior flights although in one of these the pilot spotted the problem before engaging the autopilot.
- crooked-v 8y agoFrom this other comment https://news.ycombinator.com/item?id=18408733 https://news.ycombinator.com/item?id=18408733 it sounds like a really nasty UI design that practically guaranteed the autopilot ending up in the wrong mode sometimes.
- goldie1381 8y agoIf you negate the error that the selected "altitude to reach" was zero, and lets say hypothetically it was set to 1000 ft Instead...Wouldnt autopilot control also pitch the plane in the same -I'm Imagining "controlled" manner? - 500ft in 18 seconds, thats about the same as Usain Bolt on an good day, commendable for an athletic human, somewhat another day at the office for an aircraft that's being asked by the control inputs of the autopilot system to make a dynamic change of flight direction. Just because the desired altitude was a total error, doesn't mean the plane "simply fell from the sky". The same would hold for an incorrect heading for your destination, would the aircraft heel over at breakneck speed with the wings at the vertical?...I think not.
- aussieguy1234 8y agoValidation issue?