Dear Capt Lim,
First of all, I do appreciate your work - you are doing a great job!
My question is about the auto pilot system on the Boeing and the Airbus.
On the Boeings, when the pilot engages the autopilot mode for landing, it turns off automatically if the pilot happens to push the steering (wheel? lever? - I*m not sure) down hard. It will then return to manual mode.
But on Airbus 300s the autopilot mode does not change even if the pilot does this. Is this true? I*ve heard that the 1994 China Airline Airbus 300 crash in Nagoya, Japan, was probably due to this. I have also heard that some accidents have happened with Boeings when auto pilot mode suddenly switched off during landing.
Which do you think is better?
I have flown the Boeing as well as the Airbus A300s and I prefer the philosophy of Boeing that gives the pilot ultimate control.
On the Boeing, it is true that a pilot can override the autopilot with a predetermined force applied on the controls. How? Well, the autopilot disengages immediately when the pilot manually pushes the control column, the control wheel or depresses the rudder pedals harder than usual. A warning message *AUTOPILOT DISC* is displayed in the cockpit if the autopilot is manually or automatically disconnected.
The Airbus philosophy is different. There have been some issues on the design of the autopilots on the Airbus planes. They prefer to give more control to the computer, believing that it would eliminate pilot error. However, some have expressed concern that the plane has become too sophisticated.
On 26th April 1994, A China Airlines flight took off from Taipei for Nagoya, Japan with a total of 271 persons, consisting of 2 flight crewmembers, 13 cabin crewmembers and 256 passengers (including 2 infants).
When the Airbus A300-600 was making an ILS approach to Nagoya Airport, the copilot, who manually flew the plane, accidentally depressed the GO lever. The plane automatically went to GO AROUND mode - causing the plane to increase in thrust and climb above the ideal landing profile.
The autopilot was subsequently engaged but the copilot was not aware of it and continued to fly the plane manually. In fact he was fighting against the automation! He continued to push the control column down to land but the automation countered the push by trimming off the forces.
When the captain, who was also not aware that the autopilot was still engaged, took over the hopeless situation to go around, the aircraft began to climb very steeply due to the excessive trimmed up force. It then stalled and crashed - 249 passengers, including 2 infants and 15 crewmembers were killed and 7 passengers were seriously injured. The aircraft caught fire and was totally destroyed.
Yes, the autopilot on the Boeing can fail when engaged. It is not a big deal as the pilot is always there to take over control manually. I am not clear which Boeing accidents you are referring to. On the Boeing 777, there are three autopilots and it is very rare for all the three to fail at the same time.