所谓的ABCD检
Line Maintenance Checks This type of maintenance is the most routine. Sometimes called post-flight, maintenance pre-flight, service check, and overnight checks, this is the most typical maintenance service performed on aircraft. Line checks require minimal tools and are usually done at the airport gate under the “open sky.”
Line checks happen the most frequently, as they cover basic inspection checks. Commonly, aviation maintenance technicians will inspect things like wheels, brakes, and fluid levels (oil, hydraulics) during line checks.
Performing a line maintenance check ensures an aircraft is airworthy and safe to continue service. Aircraft need line maintenance every 24 to 60 hours of accumulated flight time, but it depends on the operator of the aircraft!
A Checks The next level of checks is known as A checks. The A check is performed approximately every 400-600 flight hours, or every 200–300 flights, depending on aircraft type. A check maintenance is typically done at a hangar and can take a minimum of 10 working hours depending on the services needed. Sometimes, this maintenance is done overnight as to not interrupt the schedule that airlines keep. The frequency of this check varies by aircraft type, the flight cycle count, or the number of hours flown since the last check.
The maintenance work during A checks often covers general inspections of the interior and the aircraft hull for evidence of damage, deformation, corrosion, missing parts. Additionally, it also includes service, engine, and function checks.
Other work performed could entail things such as:
checking emergency lights lubricating nose gear retract actuator checking parking brake accumulator pressure B Checks Next, B checks are often completed during the A check phase, as airlines and operators have phased out B checks. For airlines and operators to efficiently maintain, repair, and overhaul an aircraft, some B check tasks have been absorbed into A check phases. This helps by reducing aircraft downtime, reducing time maintenance technicians work on the aircraft, improving maintenance scheduling, and implementing better usage of resources such as hangars and test equipment.
Aviation maintenance professionals perform B maintenance checks approximately every 6-8 months. It takes about 160-180 labor hours, depending on the aircraft, and can be completed within 1–3 days at an airport hangar.
Typical work completed during B checks are tasks such as checking alignment and torquing of the nose landing gear spotlight or inspecting the wheel well hydraulic tubing for condition, corrosion, and fluid leakage.
C Checks C and D checks typically fall under “heavy maintenance,” and are much more extensive than the B check. The C check requires an aviation maintenance technician to perform a deep inspection of a majority of the aircraft’s parts. Also, the C maintenance check can often take the aircraft out of service for 1–2 weeks.
This type of check often requires an aircraft to stay at a maintenance facility for the necessary space/tools/maintenance technician working hours/materials. Up to 6,000 maintenance hours are typically needed for C checks.
Aviation maintenance technicians will perform certain tasks during C checks, such as:
examination of structures (load-bearing components on the fuselage and wings) and functions for corrosion and damage checking the operation of the DC bus tie control unit in-depth lubrication of all fittings and cables There are different levels of C checks depending on the type of aircraft, much like how A checks incorporate B check tasks! For example, a schedule might have aviation maintenance technicians performing C1 check tasks on a certain day and then the next day continuing with C2 and so on.
D Checks Lastly, the so-called “heavy maintenance visit” occurs every 6-10 years depending on the aircraft. D checks are comprehensive inspections and repairs of the entire aircraft and can mean taking apart the aircraft to inspect for damage and corrosion. The process can take upwards of 30,000 to 50,000 labor hours over a period of four to six weeks.
With the entire aircraft stripped down and equipment removed, airlines often decide to refurbish aircrafts’ interiors and upgrade them altogether during D checks.
Because of the nature and the cost of a D check, most airlines plan D checks years in advance. Oh, and the cost of the entire process can cost upwards of a few million dollars!
There comes a certain point where airlines realize that the cost of repair is more than the actual cost of the aircraft. This usually happens after two or three D checks.
