Originally Posted By: azsynthetic
Originally Posted By: 757guy
Iron Mike,
Can you confirm a systems question: On the 777, when using FLCH for a descent on approach (Not that I would ever use FLCH on approach, but we can save that for another time), will the A/T's become automatically disarmed if there is no glide slope capture, i.e, no Alpha Floor protection like on other aircraft types? When/how do the A/T's arm during the approach phase?
I can answer this one since we are the builder of the 777 FMS. No, the AT will not automatically disarmed if there is no glide slope. I don't have all the details but I do know that the aircraft overshot the TOD and then tried to recapture the descent path. I believe they were OK until final approach. There should be warnings galore when speed is that low even with the AP and AT disarmed.
Azsynthetic,
No disrespect intended, but your references to TOD and overshooting are only speculation since you were not on the flight deck for Asiana 214. You yourself admitted you don't have all the details. Secondly, it is obvious from this discussion (and other discussions you have participated in the past), that you are an engineer for Bendix/Honeywell and not a pilot for a major airline. There would not be "Warnings Galore" but merely a stick shaker and a possible GPWS warning for sink rate. Knowing what the system capabilities "should do" is not the same as flying the aircraft into high density airports where we know from experience as to what works and what doesn't when given a short approach, or held up higher for lower crossing traffic, i.e., Oakland departures while SFO conducts the Bay visual.
While I agree Bendix/Honeywell makes fine products, and you are without question a fine engineer, you do not understand what really happens with ATC in day to day flight operations when flying into major airports. Many times we are slam dunked into SFO and sometimes it works best just to look out the window and fly the airplane to the runway. The airplanes have fine capabilities, but going heads down trying to program the FMC when you are high and hot only leads to further distractions when the FMC doesn't respond like you thought it would (or wasn't programmed correctly by the non-flying pilot). Last thing I want is the Non-flying pilot to start typing a bunch of changes into the FMC when we are configuring for landing in a high traffic/density location. The only change sometimes needed would be to maybe draw me a line into the FAF or runway end on the LEGS page of the FMC when given a short vector or runway change from approach or tower.
My original question directed to Iron Mike relates to his 777 Flight Operations experience, specifically this:
The 777 can catch you with what is known as the 'FLCH trap.'
When you are above the descent path and need to get down in a hurry Flight Level Change (FLCH) is a useful mode to use with speed intervention. Once in the terminal area, you normally transfer to another mode like glideslope for the ILS, VNAV for a non-precision approach, or if VFR, you can even switch off the flight directors and fly the approach using raw data.
However, in this situation the glideslope was OTS so the ILS would not have been selected or armed. If the flight directors were left on and the plane was descending at a high rate in FLCH the autothrottle would have been inhibited and so the thrust levers would have stayed at idle- 777 Flight Idle vs. Approach Idle depends on flap position.
If the Asiana was a bit high (quite normal for SFO) then regained the approach path, the rate of descent would have decreased and the speed would have started slowly reducing. With the thrust levers staying at idle, the 777 would now be in the same situation as the Turkish 737 at AMS, i.e., speed decreasing below Vref+5 and not being noticed.
The 777 has autothrottle wake up, i.e., when the aircraft approaches a stall the A/T's arm automatically and will provide up to full thrust. This gives pilots great confidence however, autothrottle wake up is inhibited while in FLCH.
So 777 pilots will be looking at this scenario and wondering if Asiana were in FLCH with flight directors on, too high, stabilized late and did not notice they were still in FLCH and that the A/T's were not keeping up to Vref plus 5 until it was too late. (The Airbus family of aircraft can also do this very thing if trying to descend to the approach path from above.)
Iron Mike, any comments on your experience would be appreciated.
757 Guy
Originally Posted By: 757guy
Iron Mike,
Can you confirm a systems question: On the 777, when using FLCH for a descent on approach (Not that I would ever use FLCH on approach, but we can save that for another time), will the A/T's become automatically disarmed if there is no glide slope capture, i.e, no Alpha Floor protection like on other aircraft types? When/how do the A/T's arm during the approach phase?
I can answer this one since we are the builder of the 777 FMS. No, the AT will not automatically disarmed if there is no glide slope. I don't have all the details but I do know that the aircraft overshot the TOD and then tried to recapture the descent path. I believe they were OK until final approach. There should be warnings galore when speed is that low even with the AP and AT disarmed.
Azsynthetic,
No disrespect intended, but your references to TOD and overshooting are only speculation since you were not on the flight deck for Asiana 214. You yourself admitted you don't have all the details. Secondly, it is obvious from this discussion (and other discussions you have participated in the past), that you are an engineer for Bendix/Honeywell and not a pilot for a major airline. There would not be "Warnings Galore" but merely a stick shaker and a possible GPWS warning for sink rate. Knowing what the system capabilities "should do" is not the same as flying the aircraft into high density airports where we know from experience as to what works and what doesn't when given a short approach, or held up higher for lower crossing traffic, i.e., Oakland departures while SFO conducts the Bay visual.
While I agree Bendix/Honeywell makes fine products, and you are without question a fine engineer, you do not understand what really happens with ATC in day to day flight operations when flying into major airports. Many times we are slam dunked into SFO and sometimes it works best just to look out the window and fly the airplane to the runway. The airplanes have fine capabilities, but going heads down trying to program the FMC when you are high and hot only leads to further distractions when the FMC doesn't respond like you thought it would (or wasn't programmed correctly by the non-flying pilot). Last thing I want is the Non-flying pilot to start typing a bunch of changes into the FMC when we are configuring for landing in a high traffic/density location. The only change sometimes needed would be to maybe draw me a line into the FAF or runway end on the LEGS page of the FMC when given a short vector or runway change from approach or tower.
My original question directed to Iron Mike relates to his 777 Flight Operations experience, specifically this:
The 777 can catch you with what is known as the 'FLCH trap.'
When you are above the descent path and need to get down in a hurry Flight Level Change (FLCH) is a useful mode to use with speed intervention. Once in the terminal area, you normally transfer to another mode like glideslope for the ILS, VNAV for a non-precision approach, or if VFR, you can even switch off the flight directors and fly the approach using raw data.
However, in this situation the glideslope was OTS so the ILS would not have been selected or armed. If the flight directors were left on and the plane was descending at a high rate in FLCH the autothrottle would have been inhibited and so the thrust levers would have stayed at idle- 777 Flight Idle vs. Approach Idle depends on flap position.
If the Asiana was a bit high (quite normal for SFO) then regained the approach path, the rate of descent would have decreased and the speed would have started slowly reducing. With the thrust levers staying at idle, the 777 would now be in the same situation as the Turkish 737 at AMS, i.e., speed decreasing below Vref+5 and not being noticed.
The 777 has autothrottle wake up, i.e., when the aircraft approaches a stall the A/T's arm automatically and will provide up to full thrust. This gives pilots great confidence however, autothrottle wake up is inhibited while in FLCH.
So 777 pilots will be looking at this scenario and wondering if Asiana were in FLCH with flight directors on, too high, stabilized late and did not notice they were still in FLCH and that the A/T's were not keeping up to Vref plus 5 until it was too late. (The Airbus family of aircraft can also do this very thing if trying to descend to the approach path from above.)
Iron Mike, any comments on your experience would be appreciated.
757 Guy
