Editor's Notebook

Annual Maintenance: Is it Enough?

Accident investigators are frustrated. When they find and pull from the wreckage the flight data recorder (FDR) and the cockpit voice recorder (CVR), they anticipate that the data and voices recorded therein will help them unravel the mysteries of catastrophe.

In too many cases, they are finding that the recordings are either unreadable or fragmentary. This is particularly so with respect to CVRs, which do not have the built-in self-test that is part of many FDRs.

So, basically, the quality of the cockpit voice recording depends ultimately on the rigor of the annual maintenance process to ensure that the CVR is working. In its recently released investigative report of the fatal crash in March 2004 of a helicopter supporting oil drilling in the Gulf of Mexico, the National Transportation Safety Board (NTSB) registered its dismay over the partial cockpit voice recording and expressed the need for improved periodic maintenance of the CVR (see related item at page 62).

On the other side of the globe, the same bitter disappointment with the CVR was evident. The Australian Transportation Safety Bureau's (ATSB) investigation of the fatal May 7, 2005, crash of a Fairchild Metroliner on approach to landing at Lockhart River in Queensland noted that the CVR tape contained "a mixture of electrical pulses and fragments of conversations, some identified from previous flights."

In other words, the CVR recording was useless, despite the universal requirement for an annual check of the CVR system for functionality. This maintenance check is not only of the CVR itself, but also of related parts, such as the cockpit area microphones, the crash sensor (i.e., the G switch), and associated wiring.

As a result of its disappointment with the CVR, the ATSB recently issued a recommendation to Australia's Civil Aviation Safety Authority (CASA), the equivalent of the U.S. Federal Aviation Administration (FAA), that cockpit voice and flight data recorders be maintained in accordance with international standards "with the aim of improving their reliability and increasing the availability of data to investigators."

And even before the ATSB investigation was complete, senators with the Australian Parliament were asking probing questions about CASA oversight of Transair, the airline to which the crashed Metroliner belonged. The transcript of the May 24, 2005, hearing of the Regional Affairs and Transport Committee reveals CASA as rather defensive about the "inspection/audit" they carried out on Transair some two months before the accident. CASA officials denied that it was perfunctory, while at the same time they acknowledged that they wouldn't have picked up on a CVR that had been malfunctioning for many months (see box).

As one wag observed, "A cursory wander through a maintenance hanger will never uncover a CVR that's inoperative, and been inoperative for months."

In the case of the Metroliner crash, the pilots would have seen ground far below just before they entered the next expanse of cloud, which was concealing a ridgeline. Because the CVR was inoperative, investigators were unable to glean what call-out's were issued by the terrain warning system or what crew comments were made in the moments before impact.

Given that the annual maintenance check does not seem to be sufficient, perhaps existing CVRs should be played back monthly rather than the presently generous annual maintenance cycle. The recording should be proven to be of the last flight, and any defects found should be reportable.. One thing is clear - a CVR, and FDR, without regular maintenance violates the precept of "trust but verify."

The Parliamentary Inquiry Into Anomalies Revealed by the Crash

Sen. Mark Bishop: ... I understand there is a question as to whether the cockpit voice recorder was operational prior to the crash of the plane. I take it that the examination of such an instrument is not a part of the safety audit.

Mr. Bruce Gemmell, CASA: It is not a routine part. ... It is not critical to (the) prevention of accidents. It is actually important once there has been one.

Sen. Bishop: ... In a sense, as a prevention into the future, I would have regarded it as critical. ... A plane having crashed to earth and 15 or 16 people having been killed - the fourth worst civilian disaster since World War II, we were informed yesterday - my questioning goes to the adequacy or otherwise of the safety audit program, no more and no less.

Chairman Bill Heffernan: If you have a requirement that once a year the flight recorder has a complete check and overhaul and the day after you have that overhaul a wire comes loose or something goes wrong, when is the next time you discover your flight recorder is not working?

Mr. Arthur White, CASA: If you are going to those sorts of depths, it could be 12 months.

From: http://wopared.parl.net/hansard/senate/committee/S8309.pd