5 ms·

I understand the bug, and it's one of the worst imaginable. Doing an unauthorized departure turn can impact terrain. At night, it may not even be noticed by th

I understand the bug, and it's one of the worst imaginable. Doing an unauthorized departure turn can impact terrain. At night, it may not even be noticed by the pilots. Source: commercially-rated pilot.

speeder 6y ago
It wasn't because software bug, but this is how "Mamonas Assassinas" died, basically during a missed approach the pilot turned the wrong direction (but with the correct radius and all) and crashed into a very tall hill near the airport.
- pravda 6y ago
  Ah yes. That was a dark day. Well, night actually. https://www.youtube.com/watch?v=PwXplj3ssNs https://www.youtube.com/watch?v=PwXplj3ssNs
zomglings 6y ago
Could you explain the bug here? It wasn't clear to me what the exact problem was from reading the article, just that it occurred under a very specific and uncommon set of circumstances.
- NikolaeVarius 6y ago
  > "This issue will occur in departures and missed approaches where the shortest turn direction is different than the required turn direction onto the next leg if the crew edits the 'Climb to' altitude field." > The FMS may change the planned database turn direction to an incorrect turn direction when the altitude climb field is edited.”
  - zomglings 6y ago
    Thanks. The summary is actually very useful. What I mean, though, was I didn't understand what the bug was - not how it manifested.
    - NikolaeVarius 6y ago
      The bug is that the flight computer could set an incorrect turn direction for a go around abort maneuver/take off procedure. https://portal.rockwellcollins.com/documents/796122/0/OPSB+Rev4.pdf/0a43ef78-ad73-5e84-03eb-b805f6edfc18 https://portal.rockwellcollins.com/documents/796122/0/OPSB+R...
    - mjg59 6y ago
      There's two components in a turn - the desired heading at the end of the turn, and the direction you should turn to get there. Setting the "Climb to" altitude appears to have cleared the turn direction information. In the absence of that, the computer will turn in whichever direction results in a shorter turn to the desired heading. This is usually what you want, but not always, so I can understand it taking a while before anyone noticed it.
    - mopsi 6y ago
      Airports have landing procedures, essentially a list of waypoints and altitudes. A landing aircraft has to fly that route down to the runway. Each list has Missed Approach Point, at which the list branches into two: landing or abort. If you are not ready to land at that point (too fast, can't see runway, previous aircraft still on the runway, etc), then you fly the abort part. Usually it tells to climb to a certain safe altitude and turn towards a waiting area for another landing attempt. These procedures can be flown manually, or activated for autopilot to fly. A bug made the autopilot turn in opposite direction to what's in the abort section. Here's a landing procedure for Helena regional airport: https://flightaware.com/resources/airport/HLN/IAP/ILS+OR+LOC+Y+RWY+27/pdf https://flightaware.com/resources/airport/HLN/IAP/ILS+OR+LOC... The narrowing beam is instrument landing system that guides you towards the runway. If you reach 4580 feet minimum altitude during approach, but can't see the runway, you must fly the abort procedure, which is drawn with dashed lines: climb immediately to 4700 feet on current heading, keep climbing to 9000 while turning to heading 021, then proceed north at 9000 on 336 degree radial from Helena radio beacon, and upon reaching waypoint WOKEN circle until further instructions. This bug could cause the aircraft turn southwest (towards mountains) instead of northeast (valley). At Helena, the bug would not reveal itself because the right turn is 114 degrees. If the procedure required to turn more than 180 degrees right, for example, 200 or so degrees right towards SWEDD, the aircraft would make a left (shortest) turn instead. Green should be flown, red would be flown: https://i.imgur.com/ojShQa2.png https://i.imgur.com/ojShQa2.png
lutorm 6y ago
It seems pretty far from "worst imaginable". I mean, it's not like it goes into an uncontrollable dive.
- redis_mlc 6y ago
  Passengers fear falling out of the sky, but that's a pretty rare thing with airplanes. A dive at altitude would give you time to react, usually minutes. Hills are invisible in the dark. Also, charted departure instructions are something you bet your life on, as well as your passengers. So if you don't trust the plates or FMS, you can't fly in IMC or at nite.
- dehrmann 6y ago
  If you still have control surfaces, is a dive at sufficient altitude ever uncontrollable? Flat spins are way scarier.
  - redis_mlc 6y ago
    The main issues are: - dive with power causing overspeed - dive causing controls to lock due to transsonic shock waves - improper recovery from a spiral dive will over-G - MCAS-style confusion - bottoming out on a phugoid oscillation - unrecoverable spins, usually in jets But in general, if you unload the wings (reduce G), then nothing breaks.

speeder 6y ago

It wasn't because software bug, but this is how "Mamonas Assassinas" died, basically during a missed approach the pilot turned the wrong direction (but with the correct radius and all) and crashed into a very tall hill near the airport.

pravda 6y ago
Ah yes. That was a dark day. Well, night actually. https://www.youtube.com/watch?v=PwXplj3ssNs https://www.youtube.com/watch?v=PwXplj3ssNs

zomglings 6y ago

Could you explain the bug here? It wasn't clear to me what the exact problem was from reading the article, just that it occurred under a very specific and uncommon set of circumstances.

NikolaeVarius 6y ago
> "This issue will occur in departures and missed approaches where the shortest turn direction is different than the required turn direction onto the next leg if the crew edits the 'Climb to' altitude field." > The FMS may change the planned database turn direction to an incorrect turn direction when the altitude climb field is edited.”
- zomglings 6y ago
  Thanks. The summary is actually very useful. What I mean, though, was I didn't understand what the bug was - not how it manifested.
  - NikolaeVarius 6y ago
    The bug is that the flight computer could set an incorrect turn direction for a go around abort maneuver/take off procedure. https://portal.rockwellcollins.com/documents/796122/0/OPSB+Rev4.pdf/0a43ef78-ad73-5e84-03eb-b805f6edfc18 https://portal.rockwellcollins.com/documents/796122/0/OPSB+R...
  - mjg59 6y ago
    There's two components in a turn - the desired heading at the end of the turn, and the direction you should turn to get there. Setting the "Climb to" altitude appears to have cleared the turn direction information. In the absence of that, the computer will turn in whichever direction results in a shorter turn to the desired heading. This is usually what you want, but not always, so I can understand it taking a while before anyone noticed it.
  - mopsi 6y ago
    Airports have landing procedures, essentially a list of waypoints and altitudes. A landing aircraft has to fly that route down to the runway. Each list has Missed Approach Point, at which the list branches into two: landing or abort. If you are not ready to land at that point (too fast, can't see runway, previous aircraft still on the runway, etc), then you fly the abort part. Usually it tells to climb to a certain safe altitude and turn towards a waiting area for another landing attempt. These procedures can be flown manually, or activated for autopilot to fly. A bug made the autopilot turn in opposite direction to what's in the abort section. Here's a landing procedure for Helena regional airport: https://flightaware.com/resources/airport/HLN/IAP/ILS+OR+LOC+Y+RWY+27/pdf https://flightaware.com/resources/airport/HLN/IAP/ILS+OR+LOC... The narrowing beam is instrument landing system that guides you towards the runway. If you reach 4580 feet minimum altitude during approach, but can't see the runway, you must fly the abort procedure, which is drawn with dashed lines: climb immediately to 4700 feet on current heading, keep climbing to 9000 while turning to heading 021, then proceed north at 9000 on 336 degree radial from Helena radio beacon, and upon reaching waypoint WOKEN circle until further instructions. This bug could cause the aircraft turn southwest (towards mountains) instead of northeast (valley). At Helena, the bug would not reveal itself because the right turn is 114 degrees. If the procedure required to turn more than 180 degrees right, for example, 200 or so degrees right towards SWEDD, the aircraft would make a left (shortest) turn instead. Green should be flown, red would be flown: https://i.imgur.com/ojShQa2.png https://i.imgur.com/ojShQa2.png

lutorm 6y ago

It seems pretty far from "worst imaginable". I mean, it's not like it goes into an uncontrollable dive.

redis_mlc 6y ago
Passengers fear falling out of the sky, but that's a pretty rare thing with airplanes. A dive at altitude would give you time to react, usually minutes. Hills are invisible in the dark. Also, charted departure instructions are something you bet your life on, as well as your passengers. So if you don't trust the plates or FMS, you can't fly in IMC or at nite.
dehrmann 6y ago
If you still have control surfaces, is a dive at sufficient altitude ever uncontrollable? Flat spins are way scarier.
- redis_mlc 6y ago
  The main issues are: - dive with power causing overspeed - dive causing controls to lock due to transsonic shock waves - improper recovery from a spiral dive will over-G - MCAS-style confusion - bottoming out on a phugoid oscillation - unrecoverable spins, usually in jets But in general, if you unload the wings (reduce G), then nothing breaks.