To: clipboard
This is the first time ever that Bell is now in a position to evaluate the situation, as everything on the helicopter is intact. During the 407 crashes, the helicopters were normally totally destyroyed, so Bell could not say what caused it. Here is the evidence. The "quick fix" that Bell promised, has failed, and all 407's should therefore regarded as suspect.
In Iran we had a pilot that was demonstrating engine failure on an AB-205 and entry into autorotation and his student didn’t respond in a timely manner. As a result the rotor speed decayed and the pilot lowered his collective and entered into a mild dive. During this time he attempted to reengage the engine but the engine needle oversped the rotor needle. He attempted restart two more times with the same result.
He entered into a successful autorotation and made a run on landing on soft earth. While the rotor was running down he was filling out his paperwork when the rotor came off the mast and in the process it hit the pylon and as it spun around the stabilizer bar punched into the helicopter just behind the pilot. This was the first Bell helicopter to have experienced a mast separation and survived. It could serve as a prime subject into the mast separation phenomenon.
In the investigation it was determined that the free wheeling unit was severely damaged most likely due to compressor stall. The maintenance records did not show any indication of this helicopter experiencing a compressor stall. Bell said that the rotor hit the pylon because the pilot used aft cyclic during the landing. To do this the structure would have to yield to allow the transmission to lean back far enough to allow the rotor to hit the pylon. There was no deformation. Bell brought in a metallurgist who said that the fracture was due to instantaneous stress caused by the blade hitting the pylon. I tried to fight this conclusion but I was overruled. We sent the mast and the stub to Agusta for testing but never got a response.
About a week later the Bell rep came up to me and asked me if I knew that the free wheeling unit as well as the entire drive line had been subjected to not just one but three compressor stalls. He knew we were investigating the incident but he never came forward nor, did he initiate any structural and dynamic checks on the helicopter as required by the maintenance manual.
Another point I came across was that our AB-206s were maintained as commercial aircraft. When the time change items were to be replaced they were then maintained as OH-58s which had higher time limits on the parts.
I brought this along with many other problems to the attention of Bell but Bell never did anything about it.
So much for corporate ethics.
