Bells and Whistles

Most of us know about the tragedy last week at Amsterdam Schiphol airport involving Turkish Airlines Flight 1951.

Nine people died, and 80 were hurt, and nothing is going to change that. Aircraft have to operate with a zero margin of error, every single time, and sometimes, terrible things happen. That is no consolation or excuse, of course.

This is what Boeing has to say, and I quote CNN:

...In a memo to pilots, Boeing says there was a malfunction in one of the plane's two altimeters, which measure the altitude above the terrain where the plane is going to land. The left altimeter was giving "erroneous" information, indicating that the plane was below 7 or 8 feet from ground level when it was actually about 2,000 feet in the air, the memo said. That caused the automatic throttles to slow the plane down. The Boeing memo notes that "the autothrottle, which uses the left radio altimeter data, transitioned to landing flare mode and retarded the throttles to the idle stop. The throttles remained at the idle stop for approximately 100 seconds during which time the airspeed decreased to approximately 40 knots below the selected approach speed."...

I will not pretend to understand aeronautical engineering or the complicated lights, knobs and buttons that we see in popular cockpit footage.

In my line of work, in oil refining, we like to say that our safety systems are comparable to those in the nuclear and airline industries. In emergency or critical process control systems, it is not unusual to have two or three instruments measuring the same thing. This is done to build in a margin of safety through redundancy. The control loops are usually designed with voting using relative and time-series comparisons. For example, if two out of three instruments suggest the need to do something drastic, an emergency system will be activated. Or, if a certain measurement has an odd deviation, a comparison of historic measurements is triggered to try to determine which instrument is faulty, and take away its voting rights.

There were two altimeters. One was taking wrong decisions on its own. We ask the pilot to be more vigilant. Any thoughts from any experts?