Deferred Maintenance: More Attention is Needed to the Safety Implications

Air Safety Week, June 26, 2000

Q & A with Bart Crotty

With nearly 40 years in the industry, Mr. Crotty presently is an independent airworthiness maintenance consultant. He also chairs the maintenance error human factors committee, International Society of Air Safety Investigators.

ASW: You believe that deferred maintenance needs more attention if air safety is to be improved further. What is deferred maintenance and why do you believe it merits more attention?

Crotty: Deferred maintenance can refer to a decision to perform unscheduled corrective maintenance later than the time maintenance personnel are first made aware of an abnormal condition. There are no regulatory agency or ICAO (International Civil Aviation Organization) definitions, regulations or advisory guidance dealing with this practice, which contributes to the problem. In fact, many persons refer to Configuration Deviation Lists and Minimum Equipment Lists (CDL/MEL) as deferred maintenance

Here's one of the big problems: In my experience, most operators do not show deferred maintenance items in the aircraft maintenance logbook. Therefore, flight crews and maintenance personnel away from the main base do not even know of the existence of deferred maintenance items, or that the aircraft has an abnormal condition that could deteriorate over time.

I have had a long standing safety concern about deferred maintenance because, in the current regulatory black hole, operators are left to develop their own philosophies, if any, on how to deal with it. Numerous times I've found outstanding maintenance items that should not have been deferred. In some cases, the item had been utterly forgotten. This is an airworthiness and a safety issue.

Further, accident investigators are not always knowledgeable about operators' deferred maintenance practices. Consequently, they may not probe the main base for lists of deferred maintenance items. In fact, neither the National Transportation Safety Board (NTSB) nor ICAO has coding to identify deferred maintenance in incident or accident reports.

ASW: How is deferred maintenance different from the well-established procedures for deferring work on items covered by configuration deviation lists (CDL's) or minimum equipment lists (MEL's)?

Crotty: These lists contain particular items that may be inoperative for a specific period of time, and the operator must obtain the approval of the regulatory agency that has oversight over his operating certificate. Operators must have written procedures and training concerning the use of the MEL and the CDL.

Deferred maintenance items can by anything else. An operator is not required to have procedures or training in deferring unscheduled maintenance. Good operators do have written policies, procedures and training in place. Others are more casual, yet monitoring and reinspection of deferred maintenance items is a must.

ASW: Can you give specific examples of situations involving deferred maintenance?

Crotty: Sure. Flight crew write-ups of systems slow to operate, such as landing gear. Or a vibration when flaps are extended. Smells of burning or burnt material. Leaks of oil, fuel, water, hydraulic fluid, of uncertain origin, with implications of contaminated systems. The real danger here is that the extent of the condition often is unknown, and this problem is compounded by under- evaluation of the possible effect on airworthiness or passenger safety by line or terminal maintenance personnel while the aircraft is in service.

ASW: Would deferred maintenance have an impact on ETOPS (extended twin- engine operations)? The FAA has given conditional approval to extending ETOPS from 180 minutes to 207 minutes, but that is based partly on more demanding MEL criteria. Is deferred maintenance an area that should be considered for ETOPS? Why?

Crotty: Without any regulatory requirements, procedures for handling deferred maintenance would be up to the individual airline. There might be individual inspectors from the regulating authority who, hopefully, would insist that an operator curtail any deferred maintenance when operating ETOPS flights.

ASW: In the course of your work as a consultant, you performed safety audits of more than 100 airlines, charter operators and repair stations worldwide. Deferred maintenance was part of your review. What did you find?

Crotty: Only about 20 percent of the organizations had good management control of deferred maintenance. By that I mean they had written policies, training, authorized personnel, and at least two departments involved. Logbooks carried deferred maintenance items. Another 30 percent of the organizations I've looked at had some management controls and training, but the level was not adequate. The remaining 50 percent had no policy, procedures or training in place. When questioned, the usual answer was that they had no problem with deferred maintenance.

ASW: If only 20% of these companies have adequate provisions for identifying and tracking deferred maintenance, should we be concerned? Why?