Originally Posted by
Zeffy
https://www.seattletimes.com/busines...urn-to-flight/
quote:
FAA guidelines say that if an emergency arises on a plane flying by autopilot, the assumption is that a pilot will begin to respond within three seconds. If the plane is being flown manually, the assumption is one second. When FAA test pilots deliberately delayed their responses in a simulation in June, one of the pilots crashed the plane.
Not a pilot. FAA's assumption that during manual flight pilots will begin to respond to emergencies within one second sounds reasonable, if we take "will begin to respond" literally.
A study about reaction times for car emergency braking found that the average driver will start releasing the accelerator about one second after another vehicle starts crossing a intersection right in front of them:
https://copradar.com/redlight/factors/IEA2000_ABS51.pdf
Accounting for some peculiarities of that experiment, overall I could say the initial reaction times of the car drivers were between 0.8 seconds and 1.2 seconds. That seems comparable to the assumption of the FAA.
However, the drivers needed an additional 1.8 to 2.8 seconds to completely release the accelerator, move their foot on the brake, and apply maximum braking pressure. So the total response time to the emergency was between 2.6 and 4 seconds. I computed those ranges as the average +/- the standard deviation.
Anyway, I think the initial response time is the wrong thing to focus on. I think much more important is what happens after the initial response. For example, on the Ethiopian flight, according to the preliminary report, this was the sequence of events during around the initial MCAS activation:
At 05:39:55, Autopilot disengaged,
At 05:39:57, the Captain advised again the First-Officer to request to maintain runway heading and that they are having flight control problems.
At 05:40:00 shortly after the autopilot disengaged, the FDR recorded an automatic aircraft nose down (AND) activated for 9.0 seconds and pitch trim moved from 4.60 to 2.1 units.
The climb was arrested and the aircraft descended slightly.
At 05:40:03 Ground Proximity Warning System (GPWS) “DON’T SINK” alerts occurred.
At 05:40:05, the First-Officer reported to ATC that they were unable to maintain SHALA 1A and requested runway heading which was approved by ATC.
At 05:40:06, left and right flap position reached a recorded value of 0.019 degrees which remained until the end of the recording.
The column moved aft and a positive climb was re-established during the automatic AND motion.
At 05:40:12, approximately three seconds after AND stabilizer motion ends, electric trim (from pilot activated switches on the yoke) in the Aircraft nose up (ANU) direction is recorded on the DFDR and the stabilizer moved in the ANU direction to 2.4 units.
So, according to the transcript "The column moved aft and a positive climb was re-established during the automatic AND motion.". But, looking at the DFDR traces, that's not exactly what happened. The pilot actually started moving the column aft almost immediately after the auto pilot disconnected, and a few seconds before MCAS activated. And he continued moving the column aft throughout the first MCAS AND movement, with some fluctuations. So, in my opinion, there was 0 response time, as the pilot responded to MCAS by continuing to do what he was already doing: moving the column aft. Of course, it's debatable if you consider that a response or not. I guess some could say he should have also started to apply ANU trim immediately, not 12 seconds after MCAS first activated, and that just continuing to move the column aft is not a response.
Also about
: "The climb was arrested and the aircraft descended slightly." The report seems to suggest that it was caused by MCAS, but according to the DFDR traces for the altitude that's not what happened. Actually the aircraft stopped climbing and started a slight descent even before MCAS activated.
And finally "The column moved aft and a positive climb was re-established during the automatic AND motion." Well, looking at the altitude DFDR traces again, I'm not sure I agree with that either. At most you could say the pilot stopped it from descending. It only started climbing a bit after they manually applied some nose up trim, then the second MCAS activation negated that, and they only resumed climbing at a significant rate after applying a larger amount of nose up trim and using the cutout switches to prevent further MCAS activations.
Unfortunately the DFDR traces don't include the vertical speed to make this more obvious, but, unlike the Lion Air accident flight and the previous Lion Air flight, that at some point behaved like a roller coaster, with huge altitude losses, overall the Ethiopian flight was neither ascending or descending a lot before and during the two MCAS activations. The altitude trace is almost flat for that interval.
So, to conclude, I think it's much more important how the pilots responded and to understand why. Not precisely how many seconds it actually took them to respond to the emergency. It doesn't matter if the response time is one second, 0.5 seconds or 0.1 seconds, if the response is letting go of the controls and closing your eyes. And yes, unfortunately some car "drivers" do that when faced with an emergency.