Non Routine, Unscheduled Maintenance

We like to think that all aircraft maintenance actions occur on a neat, tidy, scheduled basis; overnight checks, A, B, C, D, checks, progressive inspections etc. For discussion sakes, lets call this routine or scheduled maintenance. Did you know that at least 40% of all maintenance actions are non-routine, unplanned, unscheduled events? For legacy aircraft this can range as high as 60%. In other words, something broke and we did not have advance knowledge that the event was going to happen. Herein I’ll collectively call these events ‘non-routine’, and use 50% as a median basis for discussion.

What are the sources of reported non-routine events requiring maintenance?

• PIREPs: Pilot reports entered in aircraft logbooks of system malfunctions or discrepancies. These include write-ups reported by cabin crews
• Scheduled Inspections: For example, during an A check, mechanics discover leaking fluids, worn brakes, burned out light bulbs, etc. Typically, mechanics enter these write-ups on forms the industry calls ‘non-routines’.
• Events: Hail damage, FOD, bird strikes, hard landings, damage from ground equipment handlers (do you mean baggage handlers damage more than just our luggage? HA!), severe turbulence, etc.

For those of us in the supply chain, non routine maintenance is interesting indeed, for the following reasons:

• Nearly all AOG orders result from non-routine write-ups
• JIT provisioning continues to be a popular goal for suppliers, but in fact it can only practically be applied to the 50% of scheduled, known maintenance events. JIT cannot be feasibly applied to the other 50% of maintenance events, the non-routines
• Airline’s parts provisioning practices are severely challenged by non-routine events
• Every airline has some variation of a Maintenance Operations Center staffed 24/7/365 to coordinate their fleet’s maintenance needs. Most of the resources of these MOCs are dedicated to managing non-routine write-ups, and in fact most have their AOG desk located here.

Consider these:

• A “D” check may generate up to 4000 non-routine write-ups.
  Aviation Maintenance “Computing Technology: Wearable Computer,” June 2001
• “Approximately 60% of Delta’s maintenance is unplanned, a statistic that Taylor said is common in the industry, and one that must improve…We would like to flip the numbers to 60% planned and 40% unplanned.” 
  Walter Taylor, Delta Managing Director. April 2003 Overhaul & Maintenance Magazine.

As previously quoted, during a heavy maintenance check there may be hundreds to thousands of non-routines generated. Proper managing of these is the most critical aspect of the check affecting the hangar’s ability to return the aircraft on time. The management team has to carefully coordinate parts, tools, test equipment, skills and the scheduling of the tasks in the correct sequence for each write-up. Wireless technology and specialized software systems are emerging as promising solutions to the management challenges of these heavy check non-routines. Another promising emerging technology is the concept of “Predictive Maintenance”. In my next blog I hope to impart a nifty introduction to this interesting theory.