Within the scope of the investigation data from the quick access recorder29 (QAR) of the accident aircraft was also analysed. The data showed that erroneous radio altimeter heights occurred 148 times in a period of 10 months (1143 flights). Only a minor number of these occurrences were
reported by pilots as a technical anomaly in the aircraft maintenance and performance log and resulted in corrective actions as shown in table 1.
It can also be concluded that when incidents are not reported information is lost and because of that not only the operator but also the aircraft manufacturer is not made fully aware of the number of significant incidents.
Reports
The investigation revealed that reporting on problems concerning radio altimeter systems was limited. This situation was not limited to Turkish Airlines. Failure to report such problems limits the effectiveness of existing safety programmes. This can result in an inaccurate assessment of risks
by both airlines and aircraft manufacturers, limiting their ability to manage risks.
The Dekker report ignores these facts from the accident report.
Reports
The following factor also played a part. Analysis of the flight data showed that only part of the problems with the radio altimeter system had been reported by Turkish Airlines pilots.
Two further comparable incidents had occurred shortly before the accident flight. The pilots in question indicated that the irregularities could not be reproduced on the ground, and did not recur during their return flights. The crews did not, therefore, report the incident. At other airlines as well, analysis of flight data showed that the number of times when erroneous radio altimeter readings occurred in one of the radio altimeter systems was several times the number of reports actually made by pilots.
By not reporting incidents, the information is lost, with the ultimate result that neither the airline nor the aircraft manufacturer is made fully aware of the number of significant incidents. Since risk analysis is based partly on the reporting of incidents, failure to report also has an unintentional impact on the degree to which Boeing was in a position to determine the scope of a potential problem.
The Board considers that complaints and defects should always be reported timely and completely. Reports are essential to determine the urgency for realisation of solutions and by that for the proper performance of the system of safety within aviation.