June 1st, 2009, 02:14 AM, Air France 447 crashed into the Atlantic Ocean after failing to recover from a stall in a thunderstorm, killing all onboard, 228 passengers and crew members. Above are the recovery site of the flight, A330 aircraft manufactured by Airbus.
What Caused The Crash?
After studying this accident, I saw many places for improvements that were causing human error, in this case for the pilots. One of the problems was simply a lack of proper training for extraordinary flight situations. Besides that, I narrowed down the 2 root causes of this engineering-centric design flaw of the A330 primary flight display.
But first, the pitot (pee-toh) tube.
The pitot tube measures an aircraft's airspeed using the pressure created inside the tube by capturing air stream from the direction that the airplane is flying in. A330 by Airbus used these to calculate the airspeed, which was then used to yield all the other data that the pilots needed to maintain a steady flight.
In the case of AF447, the pitot tubes froze due to the supercooled water
vapors in the atmosphere while the cabin inside a thunderstorm.
1. Excessive automation & un-prompting alarms
On the left above is a flight deck of an older airplane model and on the right, that of Airbus A330 (2009). It is obvious that the analog gauges and switches have been removed. The flight display of A330 is far clean and less busy, looking like it would overall help the pilots more especially with the real-time digital displays. However, it's been oversimplified and over-automated.
When the pitot tube froze and failed to update the airspeed, all computation that required airspeed failed and started throwing errors. The problem was, all the alarms were going off simultaneously and they were not informative on which problem to prioritize. Panic was inevitable, causing the pilots to perform poorly.
2. Lack of visual and tactical feedback
One of the most common safety procedures flying through a thunderstorm is to lower the thrust, which slows down the airplane, and angle up the nose, which grants the vehicle steady altitude despite the lower speed.
A330 was lacking the tactical feedback from the controller. An analog yoke would try to regain original position, requiring the pilots to put in strength, this lack of feedback with the busy alarms caused the pilots to forget that they've lowered the thrust so the speed never recovered.
Along with this, there were no way to tell the airplane's position status, the pitch, roll, and yaw in the pitch black night sky. This caused the pilots to forget that they angled the nose up, so the airplane was fast approaching a stall.
An airplane can fly by gaining lift from the airflow around the wings as shown on the left above. However, when the angle of attack (angle between the wing and the airstream) is too high, the airflow disrupts and causes the lift to drop, and so the airplane. This drop is what's called a 'stall.'
If the altitude of the airplane is high enough, it can actually dive nose-first to regain speed and pull back up to restore cruise, however, the pilots weren't trained properly for the situation leading up to that point, and it was too late when they realized.
After analyzing the problems and design errors in the AF447 accident, I made sketches of a revised primary flight display that address those problems. This worked as a guideline for the higher fidelity solution.
Couple of the most important features to point out is the altitude diagram (5) that will later record the airplanes position and orientation from an outside view, and the lever diagram (2) that will provide visual feedback for the lever status.
I wanted to direct this project to a goal-oriented system design, where the pilots solve tasks to move on to the next goal and eventually restore cruise. This would alleviate the lack of order and provide priority and hierarchy for quick prompted reactions and waste no time in such time-sensitive scenarios.
The dial on the top right enables goal-oriented flight. When the pilot changes the dial to a different flight mode, series of actions will be prompted in order to adapt the flight to the according situation.
When actions are prompted, the according display section will have arrows, targets, or some type of signifiers for the 'goals'. Once the pilots meet those goals via manual control, safe flight is assured.
To avoid my design results being ambiguous and purposeless, I designed around the AF447 scenario. The accident was in one of the most unusual and extreme circumstances, and I thought designing for the worst case will be the solution in reach for all cases.