NTSB urges increased CVR capacity, reliability

 - May 6, 2008, 9:52 AM

The NTSB has had longstanding concerns about the lack of cockpit voice recorder (CVR) information following reportable accidents or incidents. And although there are requirements about retaining CVR information–FAR 135.151(c) and 121.359(f)–the Safety Board wants the FAA to take stronger action by requiring deactivation of the CVR after an incident or accident and requiring a functional check of the device before each flight of the day.

“The CVR can be one of the most valuable tools used for accident investigation. Unfortunately, an increasing number of safety investigations are being hampered because of a lack of CVR data,” according to the Safety Board. “Our audio laboratory regularly receives CVRs with missing or irrelevant data,” said an NTSB official.

Two primary issues cause these recordings to be deficient: the tape or memory has been overwritten by events subsequent to the incident (the most frequently recurring problem) or the recording system was malfunctioning or inoperative at the time of the incident.

In the event of a severe or catastrophic accident, the CVR is typically deactivated by a loss of electrical power, and the relevant audio that was recorded before the accident is preserved. However, many of the CVRs examined in the Safety Board’s laboratory are from incidents or accidents in which the airplane’s electrical system remained functional after an event occurred–for example, after a loss-of-control incident in which the airplane recovers.

For events such as these, the CVR needs to be deactivated promptly because of its relatively short recording duration. Most CVRs currently in service have a recording duration of about 30 min. In some cases it may take longer than 30 min to land and secure the airplane following an in-flight incident, and overwriting some or all the pertinent audio is unavoidable. In these situations, a newer CVR with a two-hour duration would provide more time to return to the airport, land and taxi to the gate before erasure of the relevant audio.

However, increased recording duration alone will not prevent the recording from being overwritten, the NTSB discovered. For example, on Dec. 27, 2000, an American Eagle Embraer ERJ-135LR encountered pitch-control problems during the initial climb after takeoff. The pilots made two attempts to land the airplane before succeeding on the third attempt. The entire incident lasted about 30 min.

The regional twinjet was equipped with a two-hour CVR, but it was not deactivated after the incident flight was completed. As a result, it continued to record, overwriting the relevant audio while the airplane remained parked at the gate with the electrical power on. According to officials, “The lack of CVR information has hampered the Safety Board’s ongoing investigation into this serious incident.”

Other incidents in which pertinent data may have been overwritten because the CVR was not shut down include an icing encounter, loss of control and substantial damage to an Embraer Brasilia; an uncommanded roll in a Bombardier CRJ; and loss of pitch control, also in a CRJ.

Amway Falcon 900B:
Inoperative CVR

In addition to the problem of overwritten recordings, the Safety Board has conducted a number of accident and incident investigations in which CVRs were either malfunctioning or completely inoperative at the time of the event. Two of the most notable examples of this problem involved an Amway Falcon 900B and a Jetstream 31.

On Oct. 9, 1999, the Falcon experienced a series of pitch oscillations while leveling off at 11,000 ft msl during a descent for landing. The aircraft load factor followed the pitch attitude and reached magnitudes between +3.3g and -1.2g, said the Board. However, the 30-min CVR tape did not contain any audio information. Subsequent testing of the device revealed an open transformer on one channel, whereas the other channels were found to be fully operational. The cause of the failure was not determined, but the Board speculated that the CVR was not fully inserted into its mounting rack, causing incomplete connections.

The other case of an inoperative CVR involved the fatal crash of a Jetstream 31, an accident in which the NTSB just concluded its investigation and released the final report.

On May 21, 2000, an Executive Airlines Jetstream 31 crashed in Pennsylvania, killing all 19 people aboard. The twin turboprop’s 30-min CVR tape contained no recorded information for the accident flight, or any other flight for that matter. “An inspection and subsequent tests of the recorder indicate that it likely had not functioned since the time it was installed, nearly three months before the accident,” according to investigators. The airplane reportedly flew an average of nine scheduled flights per week.

Meanwhile, a Comair Canadair Regional Jet suffered a “frozen yoke and no aileron control capability” while in cruise flight. The CVR was found to have an inoperative magnetic erase head and consequently could not erase any of the previous recordings.

Over the last several years the Safety Board has issued 10 separate safety recommendations to the FAA regarding poor CVR performance, but the systems continue to malfunction. In some cases, private operators may not have a principle operations inspector (POI) to review their specific CVR testing and maintenance procedures. In other cases, some operators apparently are not testing CVRs regularly, said the Safety Board, or perhaps are not using headphones to verify that the recording is intelligible. Further, flight crews may be relying solely on the CVR self-test indicator, which cannot detect many of the deficiencies the Safety Board is finding.

As with overwritten recordings, the problem of malfunctioning or inoperative CVRs is not unique to airlines. The Safety Board doesn’t believe current regulations and several alert bulletins to POIs go far enough in addressing CVR problems. For example, one current bulletin (FSAT 97-09) advises only that the CVR should be deactivated “only when the flight crew believes it is appropriate to do so.” What’s more, the NTSB said, “These problems are found with recorders from smaller, on-demand carriers, as well as private and business airplane operators.” Therefore, the Safety Board believes its recommendations should apply to Part 135 and 121 operators alike.

Below are the recommendations the NTSB recently sent to the FAA:

• Require that all operators of airplanes equipped with a CVR revise their procedures to stipulate that the CVR be deactivated (either manually or by automatic means) immediately upon completion of the flight, as part of an approved aircraft checklist procedure, after a reportable incident/accident has occurred. These procedures must also ensure that the recording remains preserved regardless of any subsequent operation of the aircraft or its systems. Any doubt as to whether or not the occurrence requires notifying the NTSB must be resolved after the steps have been taken to preserve the recording.

• Require that all operators of airplanes equipped with a CVR test the functionality of the CVR system before the first flight of each day, as part of an approved aircraft checklist. This test must be conducted according to procedures provided by the CVR manufacturer and shall include, at a minimum, listening to the recorded signals on each channel to verify that the audio is being recorded properly, is intelligible and is free from electrical noise or other interference.