Ask Captain Lim

Hi Captain Lim,

I have a somewhat neurotic co-worker who refuses to fly on an Airbus. His simple and somewhat succinct response is ?The computer makes the final decision on the Airbus and the pilot cannot override it.?

I am not a pilot or anything close to the airline fraternity but I do have some common sense. When the latest little problem happened on a Jet Blue in LA, I noticed the pilot held the nose up on the aircraft far longer than usual on a landing. At least it seemed that way to me. So if the computer cannot be overridden then how was the pilot able to hold the nose up if in fact he did.

Basically, I would like to have hear from a professional that his statement ?The computer makes the final decision on the Airbus and the pilot cannot override it.? is either true or false - with some reference to back it up.

Thanks for your time.

Mark,
Richmond BC,
Canada.

Hi Mark,

No, it is not absolutely true. Your co-worker*s response ("The computer makes the final decision on the Airbus and the pilot cannot override it") was not very specific and it could be misunderstood. Even though there is an ongoing debate as to whether pilots or a computer has the final say in a commercial jetliner when the plane approaches the design limits in an emergency, an air traveler, who is not clear as to how Boeing and Airbus apply the fly-by-wire technology on their planes, may become fearful - believing that the computer or a robot on the Airbus would completely take over control of the flying from a human being.

At the root of the controversy is, Airbus prefers computers to take over when its planes are flown towards it design limits whereas Boeing believes pilots should have the ultimate say. So, on the Boeing jets, the pilot can override their on-board computers and fly the plane manually in an emergency. (Please read one recent Boeing 777 case written by the Editor of AirlineSafety.com here)

On all modern Airbus planes, starting from the A320 up to the A340, computers prevent the pilot from climbing above 30 degrees (might lose all lift and crash) or pitch down below 15 degrees (prevent overspeed). Furthermore, it would not allow the pilot to bank or roll more than 67 degrees or make any maneuvers greater than 2.5 times the force of gravity. In other words, if a nutty pilot (or an intruder) decides to pull, push or roll the control to its maximum force, the computers would keep the plane from stalling or dropping off the sky!

Which philosophy is better? Pilots from the 2 sides have rather strong opinions - both have good and legitimate arguments. The compromise? Both Boeing and Airbus should incorporate the best of both worlds into their future cockpit designs.

Despite the diplomacy to the arguments, there are still nagging discussion by others that the Boeing 757 accident at Colombia in 1995 could have been prevented had the speed brake retracted as the pilot increased power to climb away. The Airbus A320 would have done just that but Boeing argued that it would still have hit the ridges even if the speed brakes had been retracted.

On the other hand, at least six A320 have also crashed despite the Airbus philosophy. Yes, computer sometimes becomes too smart! In 1988, one of the first Airbus 320 jets crashed during an air show in Habsheim, France. The pilots were supposed to fly low with the gears down at 100 feet. Instead, they went down to 30 feet. As far as the computer was concerned, when a plane descends below 50 feet, it assumes that the plane is making a landing. Indeed, the plane just did that and landed on top of the trees! Since then, rigorous pilot training and modification of the fly-by-wire system has reduced similar event. (Before this crash, there was belief that Airbus had finally designed a crash-proof airplane.)

You refer to the A320 JetBlue incident at LA; I believe the pilot did a manual landing and not an auto landing as he had more control of the nose wheel when he lowered it gently onto the runway.  Of course, he could override the computers for the landing. The only difference is that, instead of manually trimming the elevators as the plane progressively decelerated, the trimming of the back forces was done automatically.

In the case that you mentioned, it is not true that the computers made the final decision and could not be overridden. It could - Captain Scott Burke beautifully controlled it during the landing!