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Why is it even possible to enter a desired altitude of 0 feet into an automatic pilot? As a layman, it’s hard for me to imagine why anyone flying a 777 would wa

Why is it even possible to enter a desired altitude of 0 feet into an automatic pilot? As a layman, it’s hard for me to imagine why anyone flying a 777 would want to maintain an altitude of zero at full speed for more than a few seconds (if that).

bener 5y ago
Just a guess, is that the target altitude? Meaning they set it to zero during landing approach?
- jacquesm 5y ago
  If true that would get you a hell of a surprise when trying to land at Schiphol.
kerneloftruth 5y ago
I'm guessing it's done on approach so that the autopilot won't keep the plane from landing -- which would beg the question of why the autopilot would even be on during takeoff or landing. As one would guess, it shouldn't have been on. Insight comes from a comment in TFA: "I’m a captain at a U.S. major airline with a lot of time in 777s. Something this doesn’t mention is the that even if ground level was set into the mode control panel, the aircraft wouldn’t have descended if it was being hand flown. That means that the flying pilot here selected the autopilot on immediately after takeoff. This is unusual at Western carriers as we like to hand fly. To me this indicates a lack of experience or confidence or both."
- young_unixer 5y ago
  Lots of landings are done on autopilot.
argvargc 5y ago
This seems a very important question, and I'm not finding answers to it satisfactory. To elaborate, why isn't an autopilot "aware" of whether the aircraft is taking-off/landing or in-flight? It seems completely mad that an automated flying mode could be engaged in such an obviously suicidal way on a modern bulk carrier aircraft, without so much as a blaring warning and red flashing lights.
- krisoft 5y ago
  > It seems completely mad that an automated flying mode could be engaged in such an obviously suicidal way on a modern bulk carrier aircraft, without so much as a blaring warning and red flashing lights. You are assuming that there weren't blaring warnings and red flashing lights. Probably there were many. > To elaborate, why isn't an autopilot "aware" of whether the aircraft is taking-off/landing or in-flight? Autopilots are much simpler systems. I don't know how much you know about them, but people in the general public believe they are some AI which flies the airplane from A to B. In reality they have much more common with a thermostat than an AI. You set a target heading and the plane will bank to match it. You set a target height and the plane will pitch to match it. Yes yes, they have many modes, and some modes can do much more complicated things than these, but it is not there to replace the pilot. It is a tool to alleviate dead simple piloting tasks so the pilots fatigue less on long flights. Just as an example how simple stupid they are: You can command the autopilot to climb, and if you don't adjust the throttle appropriately (either manually, or by enabling the autopilot to adjust it) then the plane will use up all the airspeed during the climb and the autopilot will happily fly it into a stall. Also just a general rule about aviation incidents/accidents: It is a good idea to wait for a proper investigation report before running far with all kind of assumptions about what happened, and therefore what you think should be changed.
  - vultour 5y ago
    You're talking about a GA aircraft autopilot, modern airliners go way beyond that. I don't know about the 777 but I believe all newer Boeings are FBW. Airbus has been FBW since forever. I'm mostly familiar with the A320 but that things is pretty much impossible to stall under normal operation no matter how much you misconfigure the autopilot.
    - krisoft 5y ago
      No I am not only talking about GA aircraft. What do you think is going to happen if you turn off the autothrottle, manually set the throttles to idle and set the AFDS to vertical speed mode with a positive climb rate? Here[1] is an NTSB report detailing how the AFDS and the A/T work together in a Boeing 777. They enumerate several different combinations in which the autothrottle does not provide stall protection. It also calls out as contributing factor the crew’s mistaken belief that the airplane is pretty much impossible to stall. 1: https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR1401.pdf https://www.ntsb.gov/investigations/AccidentReports/Reports/...
taffronaut 5y ago
Interestingly I found that a few airports are below sea level [1], so flying at or below sea level is possible. [1] https://expertworldtravel.com/lowest-airports-world/ https://expertworldtravel.com/lowest-airports-world/
- fy20 5y ago
  The lowest is just over 1000ft below sea level. You probably don't want to be flying full speed at 0ft sea level there either.
twistedpair 5y ago
The Germanwings Flight 9525 tragedy [1] was effectuated by the suicidal pilot inputting an auto-pilot target altitude of 100ft, while flying over high mountains. The plane dutifully flew into the mountains, murdering 150 people. While there are airports with elevations lower than 0ft, this is a good design question to ask. In general, it's assumed the pilots will do the right thing to save the day, if needed. [1] https://en.wikipedia.org/wiki/Germanwings_Flight_9525 https://en.wikipedia.org/wiki/Germanwings_Flight_9525

bener 5y ago

Just a guess, is that the target altitude? Meaning they set it to zero during landing approach?

jacquesm 5y ago
If true that would get you a hell of a surprise when trying to land at Schiphol.

kerneloftruth 5y ago

I'm guessing it's done on approach so that the autopilot won't keep the plane from landing -- which would beg the question of why the autopilot would even be on during takeoff or landing. As one would guess, it shouldn't have been on. Insight comes from a comment in TFA: "I’m a captain at a U.S. major airline with a lot of time in 777s. Something this doesn’t mention is the that even if ground level was set into the mode control panel, the aircraft wouldn’t have descended if it was being hand flown. That means that the flying pilot here selected the autopilot on immediately after takeoff. This is unusual at Western carriers as we like to hand fly. To me this indicates a lack of experience or confidence or both."

young_unixer 5y ago
Lots of landings are done on autopilot.

argvargc 5y ago

This seems a very important question, and I'm not finding answers to it satisfactory. To elaborate, why isn't an autopilot "aware" of whether the aircraft is taking-off/landing or in-flight? It seems completely mad that an automated flying mode could be engaged in such an obviously suicidal way on a modern bulk carrier aircraft, without so much as a blaring warning and red flashing lights.

krisoft 5y ago
> It seems completely mad that an automated flying mode could be engaged in such an obviously suicidal way on a modern bulk carrier aircraft, without so much as a blaring warning and red flashing lights. You are assuming that there weren't blaring warnings and red flashing lights. Probably there were many. > To elaborate, why isn't an autopilot "aware" of whether the aircraft is taking-off/landing or in-flight? Autopilots are much simpler systems. I don't know how much you know about them, but people in the general public believe they are some AI which flies the airplane from A to B. In reality they have much more common with a thermostat than an AI. You set a target heading and the plane will bank to match it. You set a target height and the plane will pitch to match it. Yes yes, they have many modes, and some modes can do much more complicated things than these, but it is not there to replace the pilot. It is a tool to alleviate dead simple piloting tasks so the pilots fatigue less on long flights. Just as an example how simple stupid they are: You can command the autopilot to climb, and if you don't adjust the throttle appropriately (either manually, or by enabling the autopilot to adjust it) then the plane will use up all the airspeed during the climb and the autopilot will happily fly it into a stall. Also just a general rule about aviation incidents/accidents: It is a good idea to wait for a proper investigation report before running far with all kind of assumptions about what happened, and therefore what you think should be changed.
- vultour 5y ago
  You're talking about a GA aircraft autopilot, modern airliners go way beyond that. I don't know about the 777 but I believe all newer Boeings are FBW. Airbus has been FBW since forever. I'm mostly familiar with the A320 but that things is pretty much impossible to stall under normal operation no matter how much you misconfigure the autopilot.
  - krisoft 5y ago
    No I am not only talking about GA aircraft. What do you think is going to happen if you turn off the autothrottle, manually set the throttles to idle and set the AFDS to vertical speed mode with a positive climb rate? Here[1] is an NTSB report detailing how the AFDS and the A/T work together in a Boeing 777. They enumerate several different combinations in which the autothrottle does not provide stall protection. It also calls out as contributing factor the crew’s mistaken belief that the airplane is pretty much impossible to stall. 1: https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR1401.pdf https://www.ntsb.gov/investigations/AccidentReports/Reports/...

taffronaut 5y ago

Interestingly I found that a few airports are below sea level [1], so flying at or below sea level is possible. [1] https://expertworldtravel.com/lowest-airports-world/ https://expertworldtravel.com/lowest-airports-world/

fy20 5y ago
The lowest is just over 1000ft below sea level. You probably don't want to be flying full speed at 0ft sea level there either.

twistedpair 5y ago

The Germanwings Flight 9525 tragedy [1] was effectuated by the suicidal pilot inputting an auto-pilot target altitude of 100ft, while flying over high mountains. The plane dutifully flew into the mountains, murdering 150 people. While there are airports with elevations lower than 0ft, this is a good design question to ask. In general, it's assumed the pilots will do the right thing to save the day, if needed. [1] https://en.wikipedia.org/wiki/Germanwings_Flight_9525 https://en.wikipedia.org/wiki/Germanwings_Flight_9525