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Air Travel Delays: “Mechanical Issues”

Posted in air travel, air traveler, aircraft maintenance, airline, airline cartoon, airline delays, airline industry, airline passenger, airline pilot, airline pilot blog, airline safety, airliner, fear of flying, flight, flight attendant, flight crew, flight delays, FoF, passenger with tags , , , , , , , on April 21, 2018 by Chris Manno


“Mechanical issues” may sound like a catch-all for airline delays or, to anxious flyers, a mysterious, perhaps worrisome possibility. But it’s neither, and here’s why.

First, you have to understand two main concepts: airliners are complex mechanical wonders, and second, their maintenance and operation is very strictly and minutely regulated–and documented. This second point is essential to the aviation regulatory standard upheld by all major airlines, even though such detail must be correctly, diligently accomplished. That takes time. So, let’s walk through the possibilities.

air FA smile 001

When you board an airliner, preflight checks are ongoing. This is especially true if the aircraft has just arrived from another station (airport). As soon as the flight completion checklists are accomplished, the preflight process begins anew by the crew. To waste no time, this preflight inspection goes on even as arriving passengers deplane and departing passengers board.

The checks ensure that all operating systems on the aircraft are up to the very specific standard set by the aviation regulatory agency that oversees commercial flight operations. In the United States, that’s the Federal Aviation Administration (FAA).

Every system on that aircraft has an operational standard to determine if the aircraft is airworthy, and the jet does not move until those requirements are satisfied, right down to individual light bulbs.

Let’s look at that example: a light bulb.

If a pilot on an exterior preflight notices say, a landing light that is not working, this fact is immediately recorded in the aircraft logbook and the airline’s maintenance center is notified. The airline maintenance center will refer to the FAA specified “Minimum Equipment List” (MEL) for that particular aircraft.


Without straying too deeply into the very complex decision tree of the MEL, there are three possible outcomes for the noted discrepancy (a landing light is inoperative). First, the landing light may be replaced, tested and certified by an FAA licensed and approved aircraft maintenance technician.

Second, the item may be specified by the FAA-approved MEL as non-essential for flight under specified conditions. For example, if the aircraft is about to depart for a destination to land in daylight, the MEL may allow the flight to depart, with proper logbook documentation of the exception.

Third, the MEL may allow for a redundant system to compensate for the component. If the inoperative bulb was a wingtip position light, the MEL may allow the flight to operate with the remaining position light–if the aircraft has two and only one is required (that’s why the aircraft designer put two bulbs there in the first place).

This is the same with all aircraft systems: if there are redundant systems approved by the FAA MEL, the flight may be approved for flight with that waiver to use the backup system, once the discrepancy and waiver are properly documented in the aircraft logbook.

Of course, some essential systems have no redundancy. In those cases, prescribed repairs must be made by FAA-certified mechanics (example: a tire at the prescribed wear limit must be replaced). The discrepancy, repair and results must be properly documented before the aircraft moves.

And there are “consumables.” For example, on my flight last night, when we were doing our “Before Landing Checklist,” we noted that the engine oil quantity was at the prescribed “refill” level. That, like all aircraft specifications, is a very conservative number. It’s as if you were driving your car down the highway and noted that you had just above a half a tank of gas.

air airliner drive 001

You’d turn to your passengers and say, “The MEL says we must always have more than a half a tank of gas, so we’re going to exit the freeway and refuel now.”

In flight, I sent a data-linked message to our technical operations center noting the requirement for oil service before the next flight, which I also wrote in the aircraft’s paper logbook.

Our tech folks coordinated with the mechanics at our destination to have the oil ready and a certified mechanic to perform the refill. That’s quick and easy at one of our hub airports, because we have mechanics on staff there.

At smaller stations, airlines rely of FAA-licensed mechanics approved for contract mechanical work on specified aircraft. Of course, most airlines have access to normal consumables like oil or tires, but no one has every part on every aircraft stocked at every station.

route map NWA

If the required item is not in stock, it must be brought in, either from nearby (example: an airline’s LAX station may have an item needed for a flight out of Ontario Airport; staff can simply drive the part from Los Angeles International to Ontario). Other parts may be flown in on the next aircraft from the hub to the smaller station.

But either way, before the aircraft flies again, the prescribed maintenance procedure must be accomplished in accordance with FAA regulations and everything must be documented.

Most major airlines have this process streamlined for efficiency, like when I sent the data-linked message to prepare the arrival station for the required oil service. This was accomplished between flights with no delay. The certified mechanic noted the refill quantity and manufacturer’s details in the aircraft logbook as well as in the computerized records maintained at our airline technical headquarters.

But sometimes a procedure may take longer just by the normal time the process requires (changing a tire will take longer than changing a light bulb). Finally, the availability of mechanics at a given hour may add more time to the required procedure.

In all cases, the aircraft records must be meticulously documented, which takes time as well: approvals must be granted, remedial actions certified, and everything recorded both in the aircraft on-board paper logbook as well as the aircraft records at the airline’s technical center.

That takes time.

If the delay is predicted to be too long, we might be assigned another aircraft for the flight, which also takes time: passengers, cargo, baggage, and catering must be transferred to the new aircraft. So, if you’re waiting on board during a maintenance delay, it’s probably because swapping aircraft would take longer, or there isn’t another aircraft available.

To summarize, airliners today are complex machines with multiple parts and systems, all of which have MEL specified operating minimums. Not all replacement items are available system-wide, and and even where mechanics are immediately available, remedial processes can take time.

The “mechanical delay” we experience is due to the airlines’ unwavering adherence to very specific FAA standards.

The good news is, that’s why air travel on major airlines is as reliably safe as it is.









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