Before the pilot arrives at the aircraft, the ground maintenance crew has already completed the pre-flight inspection.

Generally speaking, aircraft maintenance management is divided into scheduled maintenance and line maintenance. Line maintenance includes pre-flight, post-flight, and transit maintenance work. Pre-flight maintenance requires two ground mechanics to spend approximately 1 hour performing checks such as tire pressure, landing gear, and electronic system power-on tests, confirming that the aircraft is sound and meets airworthiness requirements.

Scheduled maintenance refers to inspection and maintenance work that must be performed when the aircraft reaches a specific period of operation. For example, after every 500 flight hours, a general inspection of the airframe and engines is required, necessitating 20 personnel spending 6 hours to complete; this maintenance cycle occurs approximately once every month and a half. After every 4000 flight hours, a detailed inspection of the aircraft’s various subsystems is required, occurring approximately once a year.

Ground mechanics use the onboard battery to start the APU (Auxiliary Power Unit), and then check various instruments and lighting equipment.

The APU is a small turbine engine, typically installed inside the tail cone at the rear of the fuselage. The APU has its own dedicated starter motor, powered by a separate battery, and operates using fuel onboard the aircraft. The function of the APU is to provide power for various instruments and lighting equipment while the aircraft is on the ground, to provide air conditioning for the interior, and to provide compressed air for starting the jet engines. Once the aircraft’s engines are started, the aircraft’s electricity and air conditioning are supplied by the engines, at which point the APU can be stopped. However, in the event of an engine inflight shutdown (flameout), the APU becomes the primary equipment for engine restart. The image below shows the exhaust pipe of the Airbus A380 Auxiliary Power Unit, provided by Wikipedia:

Because the APU uses fuel, its noise and exhaust emissions during prolonged operation have a significant impact on the environment. Nowadays, many airports use bridge-mounted equipment (ground power) to provide electricity and air conditioning to the aircraft. This not only reduces fuel consumption for airlines but also reduces the emission of exhaust gases such as carbon monoxide, hydrocarbons, and nitrogen oxides at the airport.

After the ground mechanics complete their checks, the pilot arrives at the cockpit. The maintenance status of the aircraft, fuel and oil quantities, and other items logged in the aviation logbook are handed over one by one. For example, even if a light bulb was replaced, it is recorded along with the reason.

Afterwards, the Captain will descend a ladder approximately 5 meters high next to the Jet Bridge to the ground to perform a walk-around inspection of the aircraft.

The walk-around inspection is primarily a visual check of the aircraft’s external subsystems, performed by walking around the aircraft clockwise. The items and steps are basically as follows:

• Check if the appearance is normal, if the surface is damaged, if there are any obstacles on the control surfaces, and if there are any objects on the ground that shouldn’t be there, such as stones or forgotten tools (if these foreign objects are in front, the strong suction generated when the engines start will ingest them, causing damage to the engines).

• Nose landing gear

• Wheel chocks in place

• Radome

• Lower right fuselage, lower wing skin, Flaps and Aileron

• Right main landing gear, tires, brakes, wheel chocks

• Right engine cowling latched securely

• Foreign objects inside right engine intake

• Damage to right engine fan blades, signs of oil leakage below

• Foreign objects and residual fuel adhesion at rear of right engine

• Tail section, rudder

• Lower left fuselage, lower wing skin, Flaps and Aileron

• Left main landing gear, tires, brakes, wheel chocks

• Left engine cowling latched securely

• Left engine, same items as the right side

Additionally, there are many antennas on the aircraft fuselage, which is also an important part of the inspection. If an antenna is damaged and normal communication with Air Traffic Control is impossible, or if various navigation information cannot be obtained, the flight will be extremely dangerous.

Above is a photo I took at Nagasaki Airport showing a pilot performing a ground inspection.

I once saw a Chinese version of a 737 operating manual for Shanghai Airlines online; the section on external inspection alone was 6 pages long. If you are interested in the detailed content, you can refer to it.

It is said that a walk-around inspection of a Boeing 747-400 takes nearly 15 minutes. The aircraft is huge (over 70 meters in length, wingspan nearly 65 meters), so the long distance of walking around it is one reason. To ensure flight safety, even after professional ground mechanics have performed maintenance, regulations require that pilots must personally perform a visual inspection to achieve a multi-layered check and leave nothing to chance.

After completing the external inspection, the Captain climbs back up the ladder into the cabin and begins the cockpit inspection. At this point, there are about 20 minutes left before the aircraft departs the Jet Bridge, and the airport broadcast begins announcing for passengers to prepare for boarding.

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