
Plane drops to 928 feet after autopilot set to 0 altitude - broahmed
https://www.bbc.com/news/uk-46137445
======
mrunkel
This 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.

~~~
kss238
> 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.

If you read the UK Government report that is not what happened. The plane was
at 1500 ft when it began to descend. At 1300 ft the warning sounds activated
and the pilot reacted but it took another 300 ft of descent before the pilot
was able to fully recover from the descent.

Poor reporting from the BBC.

~~~
Retric
Only losing another 300 ft with that rate of decent _is_ a very quick
remediation. Large aircraft don't turn on a dime.

~~~
slededit
Dash-8's are pretty small though.

~~~
Retric
The industry uses Light as under 7,000kg, medium 7,000 - 136,000kg, and heavy
as 136,000kg or more for wake turbulence.

At ~15 Metric Tons (33,000lb) take off weight it's a long way from a light
aircraft. However, if your walking around these things, my personal view is a
medium is around a Cessna Citation Mustang, double that and their large, and
aircraft quickly get into huge and monsters.

------
hef19898
Reports 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.

~~~
Symbiote
For 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-
in...](https://www.gov.uk/government/organisations/rail-accident-
investigation-branch)

~~~
kevin_thibedeau
Britain's preoccupation with preserving buffer and chain couplers is not a
picture of safety.

~~~
slededit
I 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)

------
broahmed
Air 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_e7fBDYaFWG0Olwtpp...](https://drive.google.com/file/d/1P7czQkX_9_e7fBDYaFWG0OlwtppgLh9R/view?usp=drivesdk)

High resolution mirror:
[https://drive.google.com/file/d/1ulgy8cGSrG7nT1_p6PmKlxTBBi_...](https://drive.google.com/file/d/1ulgy8cGSrG7nT1_p6PmKlxTBBi_6yVLQ/view?usp=drivesdk)

Original links can be found at:
[https://www.gov.uk/government/publications/air-accident-
mont...](https://www.gov.uk/government/publications/air-accident-monthly-
bulletin-november-2018)

~~~
abluecloud
> 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
That 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.

~~~
jefurii
With a sticker saying "Beware of the leopard".

~~~
starbeast
No, not since a minor civil servant was sent armed with a cheap biro to cross
that out and write the word 'austerity', after May hunted down the leopard for
shoes.

------
post_break
Question, why is 0 a valid entry for autopilot? Would that ever be used?

~~~
Fordec
Landing?

~~~
module0000
Different autopilot for that: "autoland". Pretty neat stuff!

[https://en.wikipedia.org/wiki/Autoland](https://en.wikipedia.org/wiki/Autoland)

------
KineticLensman
To 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
From 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.

------
PhasmaFelis
The 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.

~~~
PMan74
"An Air Accidents Investigation Branch report said warnings alerted the pilot,
who fixed the error at 928ft (283m)."

It's odd, you'd think that the sensation of dropping 500ft (152m) in 18
seconds would have alerted him, especially after take off. It's hard to
visualise what that would feel like.

~~~
lbriner
You are expecting some change in G-force due to changing to AP, you don't
necessarily feel the start of the drop and once descent is consistent, it
won't feel that alarming, add to that the fact that you think the AP is
correctly set and you have confirmation bias and won't notice anything wrong.

Just goes to show that we still don't really know if we should "trust the
plane" or "trust the pilot".

~~~
xaedes
Regarding who to trust; both: trust the whole cyber-physical system. And like
OP said, the system worked as designed. The bigger system now even learns from
this and improves the existing cyber-physical system to handle such cases even
better / earlier or avoid them: "Flybe implemented remedial actions quickly in
response to the incident and our training and procedures have been amended to
minimise the risk of a reoccurrence".

------
sehugg
Is it common to set autopilot below 5,000 feet or so? Seems kind of like
setting your cruise control at 25 MPH.

~~~
mrunkel
Sure, 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.

------
x0054
This shows the necessity of reasonable defaults. Not a pilot, but somehow I
think the default setting for ALT should NOT be 0.

~~~
stouset
They 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).

------
OliverJones
The 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
Most 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)

------
0xfaded
When 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
I'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
I 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).

------
minitoar
I would think the pre take off checklist would include configuring autopilot
for your planned departure altitude/heading/whatever.

~~~
duxup
>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.

------
aussieguy1234
Validation issue?

