Aircraft Maintenance Incident Analysis

CAA PAPER 2007/04 Aircraft Maintenance Incident Analysis - Published by the Civil Aviation Authority, December 2007

Paper is an analysis of a selection of maintenance related events on jet aircraft above 5,700kg MTOW, captured and stored under the requirements of the CAA’s Mandatory Occurrence Reporting (MOR) scheme to identify trends, themes and common causes or * factors.

It presents a taxonomy that looks useful. It has three main categories:

1. Maintenance Control – An event attributed to an ineffective maintenance control
system.

2. Incomplete Maintenance – An event where the prescribed maintenance activity
is prematurely terminated. In these circumstances the correct maintenance procedures appear to have been followed but something was not removed, not fitted or not set correctly towards the end of the process.

3. Incorrect Maintenance Action – An event where the maintenance procedure was completed but did not achieve its aim through the actions or omissions of the maintainer. In these circumstances it appears that an incorrect maintenance procedure or practice was being used. This has resulted in a larger number of second level descriptors than Incomplete Maintenance, but includes the actions of not removing, not fitting or not setting something correctly by virtue of not performing the task correctly, rather than as an error of omission.

Each category is broken down further as follows, showing the results of the analysis.

1. Maintenance Control (Total 733):
* Scheduled task - 223 30·4%
* Inadequate tool control - 84 - 11·5%
* Deferred defect - 81 - 11%
* Airworthiness data - 78 - 10·7%
* Tech log - 67 - 9·2%
* Airworthiness Directive - 66 - 9%
* Modification control - 55 - 7·5%
* MEL interpretation - 37 - 5%
* Configuration control - 23 - 3·1%
* Certification - 13 - 1·8%
* Component robbery - 6 - 0·8%

2. Incomplete Maintenance (Total 602):
* Not fitted - 268 - 44·5%
* Not set correctly - 229 - 38%
* Not removed - 105 - 17·5%

3. Incorrect Maintenance (Total 1589)
* Incorrect fit - 619 - 39%
* Not set correctly - 447 - 28·1%
* Incorrect part - 160 - 10·1%
* Poor maintenance practice - 94 - 5·9%
* Procedure not adhered to - 83 - 5·2%
* Not fitted - 78 - 4·9%
* Incorrect repair - 62 - 3·9%
* Incorrect procedure - 24 - 1·5%
* Not removed - 22 - 1·4%

Unfortunatly the analysis found that information regarding underlying causes is rarely reported. This significantly limits the value of the analysis, and is something the industry needs to address.

Andy Brazier