“Air France 447 and Air Asia Q8501 are clear cases where the crash was caused either by computer problems, or because of the interface between the onboard computers and the pilots”, says Tom Dieusaert in the second part of his interview with AeroTime. What should we do to avoid these accidents in the future?

In your book you have one chapter dedicated to Air France Flight 447 and one to Air Asia Q8501, although there are more incidents you cover. Is there a particular reason you chose these two specific examples to cover in more detail?

Both are clear cases where the crash was caused either by computer problems, or because of the interface between the onboard computers and the pilots.   According to reports in Air Asia’s case, there was a maintenance problem at the root of the accident: that plane had a malfunctioning RTLU, which is the rudder travel limiter unit, one of the fly-by-wire “protections” that limit the movement of the rudder to prevent excessive rudder inputs. In itself, a malfunctioning RTLU is not critical for a flight, so it very interesting how this rather small problem amounted to a fatal crash.

One of the reasons is that the more computers you stuff in a plane, the more potential problems you can have with these computers. I quote a pilot I interviewed for my book:  “Computers solve certain problems, but they create new ones”.

Tom Dieusaert is the author of “Computer crashes: When airplane systems fail”

Most troubleshooting on the modern automated planes basically boils down to resetting of the onboard computers but this procedure has its risks. You can have “spurious faults” as well as real mechanical problems that are masked as if they were a software issue. In case of the Air France 447 of AirAsia 8501, the pilots had restarted the RTLU a dozen times during the previous months before the accident, to no avail. Two days before the accident, the maintenance crew then decided to pullout the circuit breakers of the Flight Augmentation Computer (FAC), also with no result. Finally, maintenance decided to substitute the FAC by a new one, which seemed to solve the problem temporarily. But the RTLU fault messages appeared again on the fatal flight and the pilots (probably) pulled out the CB’s again in flight, after which they lost control.

Resuming, I think, if you have a system, which is over-automated, the risk exists that you’ll think “Oh yeah, I need to restart the computer” and you don't get to solve the root problem that is behind it.

Christine Negroni, aviation journalist and author believes that the biggest error done today is putting too much tech between the pilot and the plane. Do you agree with this position or do you think there are bigger problems causing plane crashes (at least among the ones you investigated)?

I do agree. It's a bit of a philosophical question, but it’s like driving a car. Thirty years ago, we would do it completely manually and with no computer controlling us. Then maybe in 20 years from now we will have totally automated cars. Now we find ourselves somewhere in between. With aviation it’s a similar situation.  There is still manual control, but automation is taking over and telling the pilot “Do this. Don't do that…”

Aviation is one of the safest ways of transportation, but tragedies, many of which are surrounded with riddles, do happen. Hundreds of professionals dig for clues and answers during investigations that can span many years. Despite their efforts, sometimes the truth is left unearthed and the public is given an explanation that only sounds plausible.

I guess that's an awkward situation for many pilots, because they don't feel like they are directly flying the plane anymore. They have so much technology in there and maybe a lot of technology that they didn't ask for. Maybe there are “smarts” and gadgets on the plane which are unnecessary. But that is the logic of automation and the industry. Sometimes the industry puts new smarts, because they want it to sell the plane. I can imagine that pilots sometimes get overwhelmed by the quantity of technical stuff. Another important risk of automation is that pilots lose their basic flying skills.