• Home
  • /
  • How Often are Commercial Aircraft Inspected and Maintained?
how often are commercial airplanes inspected and maintained

Affiliate Disclosure: We may use affiliate links on this page that lead to Amazon or other partners. If you make a purchase after clicking on a link on this page, we may earn a small commission at no extra cost to you.

It takes a lot of training, planning, and coordination to ensure that flying commercially remains as safe as it is today. We all assume that the cockpit crew is fully trained to fly the aircraft, and knows what to do in the rare event of an emergency. We’re also told before every takeoff that the cabin crew is there “primarily for our safety”, and that’s reassuring.

But how many of us ever wonder about the aircraft itself? How old is it? Is it in good condition? Do all the systems and individual components operate properly, and when was the last time that they were inspected or repaired?

We change the oil in our personal vehicles regularly (or at least we’re advised to do so), tune-up the engine, and change and rotate the tires. Surely, in such a highly regulated industry, there must be a similar protocol for commercial aircraft. 

Let’s take a close look at the world of commercial aircraft maintenance.

Continuous Maintenance Checks for Commercial Planes

The U.S. Federal Aviation Administration (FAA) is the government agency that regulates commercial aviation maintenance programs. A CAMP, or “Continuous Airworthiness Maintenance Program”, is required to be established and approved by the FAA, well before any air carrier even flies its first flight. 

Whether the company is a legacy carrier such as American or United Airlines, or a low-cost airline like Frontier or Spirit, a rigorous CAMP program is required that spells out in extreme detail the maintenance inspections, and daily routines, for the aircraft in their fleet. These checks must be performed and signed off on by the appropriate mechanic or the aircraft’s captain prior to each and every flight departing the gate.

All commercial aircraft must undergo continuous flight line checks, known in the industry as A, B, C and D checks. The FAA sets up the regulations for these lettered checks, and it is the airline’s responsibility to make these checks occur fully, and according to the required schedule. FAA inspectors are assigned to monitor the carrier’s facilities across the country, not only at passenger terminals, but they make regular visits to the maintenance bases of each airline to ensure compliance. 

Routine Maintenance Checks

Line maintenance checks are the most common, generally performed at the gate or a nearby ramp/hangar, when the aircraft is in service. These are also called pre-flight service checks, post-flight checks, or overnight checks, depending on when the work is being done. Minimal tools are required for these checks, and they often consist of observation/inspection, rather than undertaking any physical repairs, unless something is necessary resulting from the inspection.

Aircraft items that are typically part of a line maintenance check include tires, brakes, hydraulic fluid levels, and landing gear. The checks are undertaken from 24 to 60 hours of the aircraft’s accumulated flight time, and vary according to flying the aircraft does, i.e., short haul domestic vs. international long-haul flights.

“A” Checks

Normally taking at least 10 hours to complete, “A” checks are performed every 400 to 600 flight hours, or 200-300 flights in most cases. Again, in the case of aircraft flying longer stage lengths (flight distances), this may only be 50-75 flights if, for example, the plane regularly flies from the east coast to Europe. 

Easier to manage in a hangar or on a warmer weather ramp, the “A” check often entails overnight work, and is determined by the age of the aircraft, as well as how many total flights, or hours, it has flown since the last check. 

“A” check maintenance may include aircraft interior and exterior inspections, looking specifically for any structural damage, corrosion, or parts that may have become loose during recent flights. Additionally, inspections are made of the emergency lights, nose gear lubrication and mechanical operation, and making sure that the parking brake’s air pressure is adequate. Certain servicing and engine tests may also be performed. 

“B” Checks

In recent years, stand-alone “B” checks have been commingled with “A” checks by most airlines, as they strive to minimize aircraft downtime. Historically, “B” checks were scheduled 6-8 months apart, and required up to 180 hours of labor time in a hangar. This corresponded to taking an aircraft out of commission for one to three days, depriving the carrier of much needed revenue for an extended period. 

Airlines determined that “B” check maintenance items, such as checking nose gear alignment and runway lighting, and inspecting for wheel well corrosion or hydraulic fluid leakage, could be accomplished at the same time as an “A” check. 

“C” checks

Far more complex than a “B” check, heavy maintenance “C” checks take an aircraft out of an airline’s schedule for one to two weeks, depending on how much corrective work has to be performed. Typically, multiple maintenance technicians are required for this very thorough inspection of hundreds of aircraft parts vital for safe operation. 

Depending on the type of aircraft, different levels of “C” checks are required. Designated C1, C2, C3, and so forth, as an aircraft ages, it is crucial that deep inspections of the aircraft structure, including wings and the fuselage, be meticulously performed. Aircraft technicians look for any damage to the aircraft, as well as corrosion, making repairs or reporting more extensive items to be corrected before the aircraft can be returned to service. All parts, fittings and cables are periodically lubricated at this time.

Larger airlines operate in-house maintenance facilities where their own employees perform maintenance up to and including “C” level checks. Smaller carriers typically contract with independent aircraft maintenance facilities to complete non-line maintenance activities. 

“D” checks

Both “C” and “D” checks are termed ‘heavy maintenance’ in the commercial airline industry. However, the “D” check is far and away the most comprehensive inspection of a jetliner, with the most inspections and repairs completed.

Just what does a “D” check consist of?

  • Time frame: 4-6 weeks
  • Labor: 30,000-50,000 hours (incredible, but true)
  • Cost: several million dollars, depending on the age, hours flown and number of rotations the aircraft has performed

Airlines often schedule “D” checks years in advance. After acquiring an aircraft, new or used, a timeline can be determined for when this massive check will be required. And despite the cost in both dollars and staff time, keeping an aircraft in the fleet long-term is far cheaper than purchasing new aircraft whenever a “D” check is necessary. 

During a “D” check, the entire aircraft may be dismantled, piece by piece, so that a proper inspection can be performed. Technicians will again be looking for damage and corrosion as the top priorities. Engines may be removed from the aircraft, as well as other parts, including flaps, gear assemblies, passenger and cargo doors, etc. 

Airlines will frequently take advantage of an aircraft’s downtime to schedule other needed enhancements, including the installation of new seats, changing the cabin’s seating configuration, upgrading overhead storage compartments, and having the latest in Wi-Fi systems installed. 

When an aircraft become old in aviation terms, which may be 30 or more years, then an airline may determine that the cost of a “D” check is more than the plane is worth. Much like an old car with 175,000 miles, the time comes when it just isn’t fiscally wise to make an expensive repair. 

As always, it’s all about safety

Maintaining a commercial airplane, let alone a fleet of aircraft, is an around-the-clock necessity. With thousands of moving and stationary parts, the inspection and repair process is lengthy and extremely detailed. 

By designing and following regimented maintenance procedures, airlines can keep their fleet in tip-top shape for decades. When that translates into improved aircraft reliability (fewer delays and cancelations), airlines can be trusted, and deemed highly dependable by the traveling public. 

And aircraft that are reliable translates quickly to improved profitability. Since airlines don’t have extra aircraft sitting around ‘just in case,’ having an expertly maintained fleet can be the difference between success and failure. 


Written by
Brian Fischer, Staff Writer

Fact Checked

Our team of writers and editors rigorously evaluate each article to ensure the information is accurate and exclusively cites reputable sources.

You may be also interested in...