A lightning strike on an aircraft typically has an entry and exit location. There are always at least two strike points at different areas on an aircraft. During a lightning strike on a Boeing 737, you may experience one of the following:

1. When lightning initially strikes on the forward fuselage or engine nacelles, it will move rearward over the fuselage surface or the wing surface. Then, on the wing surface, the lightning will move aft of the nacelle or aft of the extended ends of the leading-edge slats.
2. When lightning initially strikes the aft area of the empennage or wing surface, it will stay there until the lightning current stops.

A lightning strike is not only limited to the surface areas of an aircraft. The external components can also be hit and the components most likely to be hit are the wing leading edge, wing trailing edge, wingtips, engines, vertical fin tip, horizontal stabilizer tips, elevators, and nose radome.

The inspection and repair procedures for the Boeing 737 MAX meet the recommendations for the Boeing 737 Classic and the Boeing 737 NG. In December 2019, however, the Federal Aviation Administration (FAA) issued a service bulletin with recommended procedures for the Boeing 737 MAX related to lightning strikes. The document focusses on improving the electrical bonding to ensure adequate shielding of the underlying wiring from the electromagnetic effects of lightning strikes or high intensity radiated fields.

Since 2017, the lightning strike inspection on the Boeing 737 Classic (-100/-200/-300/-400/-500) or the Boeing 737 NG (-600/-700/-800/-900) is performed in 2 phases. According to the Aircraft Maintenance Manual (AMM), the 2 phases are:

1. Phase I: aircraft maintenance engineer performs a general visual inspection from the ground of the aircraft. When no damages are found, the aircraft can be released (CRS) for a maximum of 50 cycles (flights). A full inspection (phase II) needs to be performed within these 50 cycles limit.
2. Phase II: aircraft maintenance engineer performs a full visual inspection of all surfaces of the aircraft. When deviation (damage) is found, he will record the dimensions (length, width, and depth) and location (station and stringers) of the deviation on the aircraft. All this data is used to assess if the damage is acceptable or not according to the Structural Repair Manual (SRM).

After the aircraft is struck by lightning, the aircraft is grounded and thoroughly inspected for damage such as pits and burn marks by aircraft maintenance engineers to guarantee its airworthiness before the next flight. Phase I of the inspection takes 1 licensed aircraft maintenance engineer 1 hour to complete. Phase II, on the other hand, is a time-consuming process: the inspection alone requires 1 engineer for up to 8 hours to assess the status of the aircraft. To speed up the process, the inspection can be performed in 4-6 hours, with two engineers, on each side of the aircraft.

The inspection for damage caused by lightning strikes involves the use of additional equipment by aircraft maintenance engineers such as flashlight (phase I) and cherry pickers (phase II) to facilitate the assessment of the overall condition of the aircraft.  

As soon as the damage assessment of the aircraft is finished, the aircraft maintenance engineer will use the Structural Repair Manual (SRM) to determine if the damage found can be repaired following the specified procedures. If the damage is within the limits of the SRM, the repairs can start immediately. If not, a special repair procedure is required from Boeing Engineering based on the information provided by the aircraft maintenance engineer. In order to advise step-by-step on the procedure for damage repairs, Boeing Engineering needs detailed information on:

• Cause of damage, its extent, and location (dimensions and pictures).
• Proposed repair plan.
• Potential limitations (equipment, materials, etc.).
• Status of the aircraft and return to service date.
• Desired outcome (permanent, time-limited/temporary, ferry flight).

The use of drones for aircraft inspections brings game-changing results for the aviation industry and particularly Maintenance, Repair, and Overhaul (MRO) companies and organizations. All aspects of the inspection procedure, from drone flight to report generation, are automated, allowing the ground team to easily analyze and report the status of an aircraft.

In the event of a lightning strike, using a drone to perform aircraft inspection on the Boeing 737 can save up to 15 man-hours and around 7 hours of ground time. A drone can speed up the entire process of the General Visual Inspection (GVI) during the phase II, which can now be performed in minutes (60 minutes) instead of hours (8 hours). Our drone will safely fly around the aircraft and capture high-resolution pictures, allowing aircraft maintenance engineers to make a much faster damage assessment.