| FD's OFF on Airbus
Quote from Centaurus #6
“I don't know about the Airbus types but why the urgency to switch off the FD? It takes a finite time to click off the autopilot and get cracking on the avoidance and at least 2-3 seconds for the PF to lift a hand to switch off both FD.”
Great question and observation Centaurus. From your comments, you are not familiar with the Airbus models so I will give a few general tidbits for you to consider, having flown both manufacturers and currently flying the A330.
On Boeing aircraft, generally, when you disconnect the Autopilot (AP), you must also disconnect the Auto Thrust (A/T) and should likewise turn the Flight Directors (FDs) OFF. A lot of pilots simply look through the FDs on the Boeing and ‘fly the airplane.’ So, when manually flying the Boeing models (disconnecting the AP), the thrust should also be disconnected (manual) as well. However, on Airbus models and by Airbus procedure, the A/T is left engaged even with the AP disconnected. The A/T does a great job of looking after the thrust and speed for the pilot.
As pointed out above by DeeTee, on Airbus, the thrust settings will follow the FDs if left engaged during a TCAS maneuver and create all manner of havoc, so the FDs are turned off procedurally along with the AP OFF.
The way I wrote would lead you to the conclusion that you drew, but actually the whole TCAS RA procedure happens simultaneously and takes only a few seconds at best. Your point about the time it takes to turn off the FDs is not an issue because the PF is doing it all simultaneously with disconnecting the AP and beginning the pitch movement as the PNF is turning off both FDs, (unless the PF instinctively reaches up and turns his own FD off).
At any rate, this Airbus procedure did not figure into the incident at Inchon, so the pilot apparently followed the Airbus procedure, albeit too abruptly for those in the cabin without seatbelts attached.
I hope this answers your question. Regards, Magnet77 |