When we discuss any incident or mishap, we refer to possible causes as “contributing factors.”
You can’t say one single thing caused the incident, because there are so many other decisions and influences. Even seemingly basic things are considered, like if the weather was uncomfortably hot for the people involved.
Let’s pick out some of the possible contributors to the X-31 aircraft loss.
- The X-31 test program, across multiple aircraft and over 550 flights, had not encountered any significant issues and was overall very successful. This fact, as well as this being the final flight of aircraft number one, could have led to the team being less vigilant of possible issues in testing.
- The aircraft was operating with a newly installed, alternate air data probe that had a severe environmental vulnerability. That may not have been made clear to the entire team.
- The pitot heat was inoperable, but the switch for it had no indication of this—there was no sticker or placard installed that read NO HEAT. And as one of the interviewees mentions, though they had provided notice of the lack of pitot heat to the entire team, there was never a check to make sure everyone fully understood it.
- Atmospheric conditions on the day of the flight made ice buildup possible, if not probable. Note that this was paired with a pitot probe that was more vulnerable to icing than the regular pitot probe.
- There were clear communication breakdowns between personnel. Due to radio issues, the chase plane’s pilot was unable to hear the X-31 pilot speaking. And when possible issues were communicated from the X-31 pilot to the control room, the discussions in the control room did not include the pilot.
- When first alerted to the airspeed problem, the engineers may have become overly focused on troubleshooting the issue as if the X-31 had already safely landed.
There are two main threads that I want you to take away from this: communication and vigilance.
The comms breakdowns between the X-31 pilot, chase pilot, and control room likely significantly contributed to what happened on that day. One of the communication links was entirely broken due to hardware problems, and another (X-31 pilot to control room) was unreliable. We can’t say that having clear three-way communication would have prevented this mishap entirely, but there’s no doubt it would have helped.
I hesitate to call it complacency, but the team likely thought of the X-31 as a regular airplane on routine flights. Remember, this was an experimental technology demonstrator. Some of the wariness and uncertainty that were no doubt present during its first flight should have existed during its last.
On top of this, at all times the focus should have been on the safety of the aircraft and its pilot. When an aircraft is airborne and experiencing a problem is not the time to think through possible causes. Determine and take appropriate mitigating actions, bring the pilot and aircraft home, and then do the engineering investigation.
We don’t want a near-miss or an accident to happen. But when one does, it becomes an excellent lesson for the entire industry, and a reminder that we are all responsible for breaking the chain when we have the chance.