"Chesley "Sully" Sullenberger, Captain of US Airways Flight 1549 that ditched in the Hudson River on January 15, 2009, said in a Google talk that the landing could have been less violent had the anti-phugoid software installed on the Airbus A320-214 not prevented him from manually getting maximum lift during the four seconds before water impact."
That's pretty interesting. Should pilots be able to disable all control-limiting software manually?
It’s a fundamental difference between how Airbus and Boeing approach flight controls. Airbus take the view that pilots should never be able to command an action the aircraft thinks is dangerous. Where as Boeing believe that pilots have ultimate authority to command the aircraft to do anything, regardless of if aircraft thinks it’s dangerous (obviously the aircraft provides warning etc, but they can ultimately be overridden and ignored).
In a little more detail, Airbus systems take pilot inputs, interprets what the pilot wants to achieve, then commands control surfaces to produce that outcome. Applying limits etc to ensure that flight limits aren’t exceeded. The end result is that pilot inputs are somewhat loosely correlated to control surface outputs, compared to traditional fully mechanical system.
Boeing on the other hand tries to as tightly a possible map pilot inputs to control surface outputs, mimicking a pure mechanical system (despite being fly-by-wire, like Airbus). But provides force feedback to the pilot via input controls to indicate, but not completely prevent, that the pilot is approaching or about to exceed flight control limits.
> Boeing on the other hand tries to as tightly a possible map pilot inputs to control surface outputs, mimicking a pure mechanical system (despite being fly-by-wire, like Airbus). But provides force feedback to the pilot via input controls to indicate, but not completely prevent, that the pilot is approaching or about to exceed flight control limits.
Regardless of whether that was ever true, it was no longer so once we had Boeing using an aggressive MCAS to get the 737 MAXes certified.
This alleged dichotomy between manufacturers was addressed in a comment to an Aviation Stack Exchange question [1]: "Airbus philosophy is not that if computers cannot save the aircraft, pilots cannot either. That is nonsense, and internet fodder. Control laws can be changed/downgraded even w/out pulling circuit breakers, though procedure is indeed complicated and involves pushing two buttons. Airbus recommends using appropriate amount of automation and taking control when things don’t go as expected" [Radu094] (unfortunately, the subsequent discussion is no longer available, at least on this site.)
There was a concern that pilots had not been made aware, through their training, that the system might constrain their actions in this situation, leading to the NTSB issuing this recommenation:
Require Airbus operators to expand the angle-of-attack-protection envelope
limitations ground-school training to inform pilots about alpha-protection mode
features while in normal law that can affect the pitch response of the airplane. [2]
As noted, the flight crew was not able to initiate part 2 of the Engine Dual Failure checklist, which contained airspeed guidance for pilots to follow if an engine restart is considered impossible and a ditching is anticipated. The checklist states that, when an engine restart is considered impossible, the optimum airspeed at which to fly is the green dot speed.
Despite not reaching this portion of the Engine Dual Failure checklist, the captain stated during postaccident interviews that he thought that he had obtained green dot speed immediately after the bird strike, maintained that speed until the airplane was configured for landing, and, after deploying the flaps, maintained a speed “safely above Vls,” which is the lowest selectable
airspeed providing an appropriate margin to the stall speed. However, FDR data indicated that the airplane was below green dot speed and at Vls or slightly less for most of the descent, and about 15 to 19 knots below Vls during the last 200 feet.
The NTSB concludes that the captain’s difficulty maintaining his intended airspeed during the final approach resulted in high AOAs, which contributed to the difficulties in flaring the airplane, the high descent rate at touchdown, and the fuselage damage. (See additional discussion in section 2.7.1.)
This is a seemingly simple yes/no question but you have actually entered a forest.
Most things can be disabled by a pilot. Airliners are marvels of engineering and often contain a data center to maintain control of the aircraft [1]. There is only so much flexibility you want to create for your customers… and the goal is to simplify operations with safety in mind.
avianlyric|1 year ago
In a little more detail, Airbus systems take pilot inputs, interprets what the pilot wants to achieve, then commands control surfaces to produce that outcome. Applying limits etc to ensure that flight limits aren’t exceeded. The end result is that pilot inputs are somewhat loosely correlated to control surface outputs, compared to traditional fully mechanical system.
Boeing on the other hand tries to as tightly a possible map pilot inputs to control surface outputs, mimicking a pure mechanical system (despite being fly-by-wire, like Airbus). But provides force feedback to the pilot via input controls to indicate, but not completely prevent, that the pilot is approaching or about to exceed flight control limits.
https://en.m.wikipedia.org/wiki/Flight_control_modes
mannykannot|1 year ago
Regardless of whether that was ever true, it was no longer so once we had Boeing using an aggressive MCAS to get the 737 MAXes certified.
This alleged dichotomy between manufacturers was addressed in a comment to an Aviation Stack Exchange question [1]: "Airbus philosophy is not that if computers cannot save the aircraft, pilots cannot either. That is nonsense, and internet fodder. Control laws can be changed/downgraded even w/out pulling circuit breakers, though procedure is indeed complicated and involves pushing two buttons. Airbus recommends using appropriate amount of automation and taking control when things don’t go as expected" [Radu094] (unfortunately, the subsequent discussion is no longer available, at least on this site.)
There was a concern that pilots had not been made aware, through their training, that the system might constrain their actions in this situation, leading to the NTSB issuing this recommenation:
Require Airbus operators to expand the angle-of-attack-protection envelope limitations ground-school training to inform pilots about alpha-protection mode features while in normal law that can affect the pitch response of the airplane. [2]
[1] https://aviation.stackexchange.com/questions/52147/why-cant-...
[2] https://www.ntsb.gov/investigations/AccidentReports/Reports/... Page 124
mannykannot|1 year ago
2.3.3 Descent and Ditching Airspeed
As noted, the flight crew was not able to initiate part 2 of the Engine Dual Failure checklist, which contained airspeed guidance for pilots to follow if an engine restart is considered impossible and a ditching is anticipated. The checklist states that, when an engine restart is considered impossible, the optimum airspeed at which to fly is the green dot speed.
Despite not reaching this portion of the Engine Dual Failure checklist, the captain stated during postaccident interviews that he thought that he had obtained green dot speed immediately after the bird strike, maintained that speed until the airplane was configured for landing, and, after deploying the flaps, maintained a speed “safely above Vls,” which is the lowest selectable airspeed providing an appropriate margin to the stall speed. However, FDR data indicated that the airplane was below green dot speed and at Vls or slightly less for most of the descent, and about 15 to 19 knots below Vls during the last 200 feet.
The NTSB concludes that the captain’s difficulty maintaining his intended airspeed during the final approach resulted in high AOAs, which contributed to the difficulties in flaring the airplane, the high descent rate at touchdown, and the fuselage damage. (See additional discussion in section 2.7.1.)
https://www.ntsb.gov/investigations/AccidentReports/Reports/...
imoverclocked|1 year ago
Most things can be disabled by a pilot. Airliners are marvels of engineering and often contain a data center to maintain control of the aircraft [1]. There is only so much flexibility you want to create for your customers… and the goal is to simplify operations with safety in mind.
[1] https://youtu.be/AAf1SePrKLc
magic_smoke_ee|1 year ago
loloquwowndueo|1 year ago