A while back I wrote about the spiral dive and crash of SilkAir Flight 185 in the post, What if they crashed? That particular post also has a full length documentary concerning the crash and subsequent investigation. During the investigation into this accident, investigators discovered that both the CVR and flight data recorder had stopped recording prior to the incident. The conclusion of the NTSB was that the pilots, most likely the captain, purposely pulled the circuit breakers to those recording devices before committing suicide.
Now the recorders didn’t stop recording at the same time. Several minutes passed between the two failures. The NTSB did not give any explanation as to why the captain of the flight would pull one circuit breaker and then wait another eight minutes before pulling the second circuit breaker.
Unlike the CVR, which records only the last 30 minutes (longer on newer aircraft), the FDR records the last 25 hours. An independent investigation conducted by a lawyer representing families of the Flight 185 passengers discovered that the flight data recorder had stopped recording on a number of occasions during that 25 hour recording. So the fact that it stopped recording just prior to the upset is not so mysterious or damning.
Around the time of the TWA 841 incident, United Airlines had an incident that required the pulling of the CVR. They found that the CVR was not working correctly. That discovery led to a maintenance review of all of the CVR’s in the United fleet. Investigators found CVR anomalies fleet wide.
The 727 involved in the TWA 841 incident was fourteen years old. The CVR and FDR were original equipment. The official NTSB report contains the following statement: “Tests of the CVR in the aircraft revealed no discrepancies of the CVR’s electrical and recording system.” The truth is that no tests were done on the CVR in the aircraft or after it was removed from the aircraft. You can learn more about this in the post, The story of the CVR and the man with blinders. In reviewing the civil trial held in May of 1983, I came across the testimony of George Andre, a TWA pilot who flew the same aircraft involved in TWA 841 weeks after repairs had been made in Kansas City. Attorney Don Mark is asking the questions on redirect.
Q. Then finally, Captain Andre, you were asked a question yesterday with respect to the flight data recorder foil from your May 12, 1979 flight. Do you recall that question?
A. Yes, sir.
Q. Has that tape been retained?
A. Yes. I found out since yesterday that the tape is retained at TWA.
Q. As a matter of fact, it’s also been examined, hasn’t it?
A. Yes, I believe it has.
Q. Did you find out that there was a mechanical problem with one parameter of the flight data recorder?
A. Yes, I found out that the vertical acceleration trace did not record on that flight data recorder.
Mark: Thank you, sir. That’s all. (Testimony of George Andre May 24, 1983 P 1417.)
So now we have evidence that the FDR on TWA 841 had experienced an anomaly. Taken alone, it doesn’t say anything about the functionality of the CVR. But when you combine that fact with other facts related to the CVR: the electrical wiring around the gear was damaged, the plane was fourteen years old, the experience of United Airlines, the statements of the crew whom don’t remember erasing the CVR, and you have to concede that the possibility that the supposed bulk erasure of the CVR was not an intentional erasure by anyone but possibly a problem with the recording device itself.
After making this post I realized that this clue may not be as significant as I first thought. The original FDR was removed from the plane the night of the accident. This means that the FDR on the plane on May 12 was either a replacement or the original recorder with a new foil. My guess is that it was a different FDR. Even if it was the same FDR like the faulty acceleration trace could have been attributed to damage done during the high G dive. There was plenty of evidence that the stylus’s on the original recorder were effected by the nearly 6 Gs the plane experienced. The only conclusion that could be drawn from this additional clue is that the equipment used during this timeframe was susceptible to anomalies.