AWB
34-7 Issue 1, 22 July 2002
Erroneous Air Data Indications
Applicability
All Pitot Static Systems
Who should read this
All maintenance personnel, pilots and persons responsible for developing and managing the Aircraft Maintenance Program/Maintenance Schedule (AMP/MS)
Background
A recent report issued by the Aircraft Accident Investigation Board (AAIB) in the Republic of the Philippines has identified erroneous air data indications as a significant contributing factor to an accident involving a MD-11F aircraft that occurred at Subic Bay in October of 1999.
The cause of the erroneous indications was due to blocked pitot probe drain holes. The AAIB has recommended that operators incorporate detailed inspections of the pitot tubes including the drain holes at a suitably frequent interval. Boeing has since updated the inspection requirements to ensure that the drain holes are inspected at an interval that does not exceed 650 Flt Hrs.
Other significant factors were related to flight crew response to air data anomalies and are not within the scope of the purpose of AWB's, however it is recommended that all pilots consider reviewing their understanding of the requirements.
Recommendations
Maintenance Personnel
Ensure that where inspections of pitot static probes and ports are carried out that the inspection is sufficiently detailed to ensure that any associated orifices are unobstructed and any damage is within maintenance manual limits.
Flight Crew
Ensure that where access is available the pre-flight or transit inspections of pitot static probes and ports are carried out that the inspection is sufficiently detailed to ensure that any associated orifices are unobstructed and any damage is assessed by appropriately rated maintenance personnel to be within maintenance manual limits.
AMP/MS
Ensure that inspection intervals and instructions are adequate.
Comments
There have been a number of similar occurrences world wide in both air transport and private operations that identify a common problem. Simple cost effective solutions are available to reduce the number of related incidents/accidents, including;
- The use of pitot covers and static port plugs with remove "BEFORE FLIGHT" streamers; and
- Adequate and appropriate inspections.