The recent grounding of 128 planes of the Southwest Airline fleet along with a number of private aircraft accidents have placed a renewed emphasis on aircraft inspections. During the course of this blog, we will examine the inspection process, as well as the human factor.
While many processes in today’s aviation are performed electronically, the inspection of an aircraft is still largely done by visual observation. An aircraft inspection may range from a casual walk around the plane to a detailed inspection involving a complete removal of aircraft components, utilizing complex inspection aids. The first step of conducting an aircraft inspection involves collecting the required forms and reference materials from which to document the inspectionThe aircraft log books must be reviewed to provide background information and a maintenance history of the aircraftChecklists are utilized to ensure all items are included, appropriate to the scope of the inspection. Additional publications provided by the aircraft manufacturer and the Federal Aviation Administration are useful guides for inspection standards. Conceptually, aircraft inspections may be planned on either a flight hours or a calendar basisAircraft functioning under the flight hour system are inspected when a specified number of flight hours are accumulated. The flight hour system requires more documentation than the calendar inspection, as well as placing limits on the number of hours an aircraft may be flown. Different parts and operating systems on a plane may also have varying hour limits between inspections. The calendar inspection system establishes a regular interval between aircraft inspections, specifying a given number of weeks between each inspection. The calendar system is both simple and efficient, with scheduled replacement of components with hourly operating limits replaced on the date nearest the hourly limit.
The criteria governing the airworthiness of a plane is specified by the Code of Federal Regulations, which prescribes maintenance and flight operations standards. Title 14 of the CFR establishes the requirements for annual and 100 hour inspections. Private aircraft with less flying hours are subject to annual inspections while commercial planes must have a complete inspection every 100 hours. While both inspections are identical in detail, there a few differences. A certified air frame and power plant maintenance technician can perform a 100 hour inspection, while an annual must be performed by a certified air frame and power plant maintenance technician with inspection authorization. Also, the 100 hour inspections are more rigid in their maintenance schedules, allowing only a 10 hour overflight beyond the 100 hour limit to the inspection site. Since annual inspections may be quite extensive and detailed, the progressive inspection program was developed. The progressive inspection program divides the inspection process into four to six phases, the completion of which amounts to an annual inspection. Under the progressive program, an inspection phase is usually completed within a couple of days – minimizing the downtime of an aircraft. If the required phases are not completed within a twelve month period, the remaining phases must be completed before the end of the 12th month from when the first phase was completed. Owners and operators contemplating a progressive inspection program must submit a written request to the FAA Flight Standards District Office having jurisdiction over where the applicant is located.
No matter what type of inspection program an airline or operator utilizes, human error is always a factor. Historically, human error studies have emphasized flight crew performance with a more recent emphasis on air traffic controllers. Air safety studies have largely neglected human factor issues affecting the performance of aircraft maintenance personnel. This has been a serious oversight, since human error in aircraft maintenance has had an equally dramatic effect upon the safety of flight operations as pilot or air controller error. Both aircraft maintenance and inspection tasks can involve a variety of duties, creating an environment for error. Maintenance personnel frequently work under time pressures, especially in high traffic segments, in which the carrier seeks to maximize profits while minimizing aircraft turnaround times. Aircraft maintenance technicians are increasingly servicing fleets which are increasing in age, with many planes in service for over twenty years. These aircraft require an intense inspection regimen to detect signs of fatigue, corrosion and general deterioration. Concurrently, new technology aircraft are entering service with the world’s air fleets, with features such as composite materials, environmentally friendly engines and built-in diagnostic equipment. The need to maintain air fleets of multiple technology tiers will require both a highly skilled and educated technical force to meet present and future demands of the aviation industry.