Recommendation R19980252

Recommendation issued to: Civil Aviation Safety Authority

Recommendation details
Output No: R19980252
Date issued: 16 February 1999
Safety action status:

Output text

The Bureau of Air Safety Investigation recommends that the Civil Aviation Safety Authority review the maintenance inspection requirements of the C402 flap actuator in order to assess the adequacy of flap actuator maintenance.

As a result of the investigation into this occurrence, the Bureau simultaneously issues recommendation R980251 to the Cessna Aircraft Company:

"The Bureau of Air Safety Investigation recommends that the Cessna Aircraft Company review the design and maintenance inspection requirements of the C402 flap system/actuator in order to assess the adequacy of flap actuator maintenance".

Initial response
Date issued: 19 April 1999
Response from: Civil Aviation Safety Authority
Action status: Closed - Accepted
Response text:

The report provides a thorough analysis of the problem, with obvious evidence of extensive research.

The actuator is confirmed to be On-Condition by the aircraft manufacturer. The manufacturer's recommended maintenance program includes a system check every 200 hours, and the Cessna aging aircraft Continuing Maintenance Program calls for a visual inspection of the flap system every 2,500 hours. Schedule 5 does not require a specific inspection of the flap actuator.

The failure mode of broken drive gears is to either jam the flaps in a fixed position or to allow the flaps to instantly retract in-flight. The jammed flaps situation is not of specific concern, as the aircraft certification requirements include to be able to land without flaps. However, an instantaneous flap retraction could be more significant, especially at critical periods of flight. Instantaneous flap retraction may have been considered an unlikely event and not specifically tested during certification of the aircraft

Unfortunately, if the failure was caused by mechanical overload, a regular maintenance program would not prevent failures unless the inspection was conducted at very frequent intervals. This is emphasized by the variable times when failures have occurred. An effective maintenance program could. therefore be very expensive. There are a number of these aircraft and related aircraft models on the Australian Register.

We are seeking further information from the pilot who encountered this event to ascertain the effect of the flap retraction. Due to the time elapsed since the incident, and considering that the aircraft has since been sold, we may not be able to accurately determine the affect on the aircraft when the flaps retracted. Any additional information you have from the incident report would therefore be appreciated.

The result of questions you have asked the manufacturer would also be of value in making a final determination in regards to this recommendation.

In summary, the recommendation has merit, but has not been implemented pending receipt of further information. Advice of the manufacturer's comment would be appreciated when received.

Last update 01 April 2011