What happened in Reno?

(cross posted from the day job)

In the aftermath of last fall's tragic crash at the air races in Reno, some "experts" suggested the age of the pilot was a contributing factor in the disaster that killed 10.

Today, the National Transportation Safety Board released its recommendations as a result of the crash and none of them involve the age of the pilot. Instead, it focuses on the decisions he made months before the race.

"Our investigation revealed that this pilot, in this airplane, had never flown at this speed on this course," Chairman Deborah Hersman said.

The NTSB recommendations center on the fact that the air racing officials exercise no or little control over the designs airplane owners resort to in order to wring as much speed out of the planes as possible.

In its letter to race organizers today (available here) , the NTSB said the organizers relied only on the say-so of the pilot that the plane was safe:

The NTSB notes, however, that such a statement does not necessarily mean that the airplane, with its modifications, was evaluated while operating within the speed and flight regimes that would be encountered on the race course. Review of the airplane's maintenance records and documentation associated with its experimental airworthiness certificate found no evidence that any engineering evaluation of the modifications had been performed. Such an evaluation would provide an opportunity to identify potential unintended consequences of the modifications. For example, shortened wings require higher angles of attack, which, if executed at higher speeds, raise the possibility of destabilizing effects or control anomalies. The use of one tab to drive both elevators raises concerns about structure and flutter; the pinned elevator tab also raises concerns about stiffness and flutter. The addition of weight behind the hinge line of the elevator tabs may decrease the flutter margin.

It's significant the NTSB focused on the trim tab on the elevator. Here's what I wrote last year:

I have no idea what happened, but it was pretty clear to me by watching the video that it involved the area of the elevator -- the control surfaces on the back of the tail that control aircraft pitch. Am I right? I don't know.

Since then, there's been a focus on the "trim tab," a small piece along the elevator that a pilot can adjust to set a plane's pitch without needing to exert control input via the yoke so intensely.

The NTSB hasn't yet determined the specific cause of the crash, but it appears heading for a ruling that "flutter" is the culprit. Flutter is a frequency that oscillates perpendicularly, is eventually transferred to sound waves that literally rip a plane apart.

The agency said it's concerned that the Reno Air Racing Association didn't analyze any of the plane's modifications to ensure that it could safety operate over crowds.

The NTSB also urged a change in the course design and confirmed that the pilot probably blacked out because of high g forces. It recommended g-force training for all pilots and a requirement they wear g suits to minimize the effects of decreased blood flow to the brain.