From A To D – How Aircraft Maintenance Checks Differ

Aircraft require tons of maintenance. Every single day, an airplane receives some sort of care to keep it tuned and ready to fly. The aviation industry is all about safety, and it can’t tolerate the absence of an effective inspection and maintenance program. If airlines worldwide weren’t checking their fleets constantly, there would be an increased chance of failure. But how do airlines define maintenance? What’s an A Check? Why is there no longer a B Check? Let’s investigate further. 

Maintenance Volaris
Airplanes receive maintenance on a daily basis. Photo: Daniel Martínez Garbuno/Simple Flying.

Maintaining an aircraft is a never-ending process

As Qantas said a few years ago, “it’s easy to forget when you board a modern jet aircraft that you’re stepping onto one of the most complex machines ever created.” 

Any airplane is a tuned machine that has primary systems and backup systems. They allow the aircraft to fly increasingly longer distances and be one of the most efficient technology pieces ever built. That’s why you still see a lot of old aircraft still flying around. If a plane from the 1950s has proper maintenance, it can still fly. 

Before the introduction of large jet aircraft, like the Boeing 707 and the DC-8, maintenance was done by pilots and mechanics based on their individual experiences. They created simple programs without proper analysis. However, the appearance of airlines and jetliners shed light on the necessity of regulation and a maintenance program development. 

As any technician knows, every aircraft on commercial service receives line maintenance around the clock. This type of maintenance is the most routine, sometimes even called post-flight or pre-flight. It is usually done at the airport gate and covers basic inspection checks. Engineers and technicians check wheels, brakes, and fluid levels, for example. 

Maintenance Aeromexico
Airlines do their own maintenance or, sometimes, use specialized companies like MROs. Photo: Daniel Martínez Garbuno/Simple Flying.

A Checks and B Checks

Then, every eight to 10 weeks, airplanes need what is known as the A Check. In this process, technicians change filters, check, and lubricate critical systems. They also give a detailed inspection of all the emergency equipment. The A Check takes between six and 24 hours on a narrowbody aircraft. 

According to the National Aviation Academy, the A Check is performed approximately every 400 to 600 hours or every 200 to 300 flights. 

Meanwhile, there used to be a B Check. Operators have phased out these Checks and merged them into the A Checks. The B Check used to be made every six to eight months. It took up to 180 labor hours and could be completed within one to three days at an airport hangar. 

Maintenance Viva Air
A well-tuned aircraft can fly for decades. Photo: Daniel Martínez Garbuno/Simple Flying.

C Checks and D Checks

The heavy maintenance is much more extensive than A and B Checks. The C and D Checks take out the aircraft of commercial services for several weeks. 

The C Check happens every 18 months to two years. It takes three weeks. Recently Argentinian carrier Flybondi sent its last Boeing 737 to a C Check in Mexico. It currently has no operational aircraft to fly. 

A C Check takes up to 6,000 maintenance hours. Technicians perform specific tasks such as examination of structures and in-depth lubrication of fittings and cables. 

Finally, the D Checks are the heaviest maintenance visit of them all. It occurs every six to ten years, and it involves comprehensive inspections and repairs of the entire aircraft. Technicians basically dismantle the airplane and put it back together. As Qantas said, 

“Everything in the cabin is taken out (seats, toilets, galleys, overhead bins) so engineers can inspect the metal skin of the aircraft, inside out. The engines are taken off.”

Also, they remove the landing gear and aircraft systems, which are checked, repaired or replaced, and reinstalled. 

The D Checks take about three to six weeks and costs several millions of dollars. Once it is done, the plane is almost like a brand new aircraft. However, when an aircraft receives between two or three D Checks, it may become more costly than the plane’s actual value. Then, it is time to retire the aircraft (or resell it). 

What do you think of maintenance checks? Let us know in the comments.