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Do You Know About a 100-Hour Inspection?

With all of the inspections an individual aircraft undergoes throughout its life, the 100-hour inspection is one of the most crucial – especially if you’re flying non-crew passengers. This type of inspection ensures that your plane is in good shape every 100 hours of flight, stopping small problems before they endanger anyone on board or on the ground.


But, of course, there’s much more to it than that. Here’s what you need to know about a 100-hour inspection. Let’s get started!


A 100-hour inspection is an essential analysis of any aircraft that carries passengers other than the crew members. In other words, aircraft used for commercial purposes are subject to this assessment at 100-hour intervals of flight time. An allowance of an extra 10 hours is provided to allow for the aircraft to be flown to the place the inspection will be taking place. An Airframe and Powerplant (A&P) mechanic carries out the 100-hour inspection.




We know that a 100-hour inspection is necessary for an aircraft for hire. On the other hand, an annual inspection is a yearly evaluation of commercial and private aircraft. The annual inspection should be carried out by an A&P mechanic that has Inspection Authorization (AI). Should your annual inspection timeframe lapse before you get it renewed, you’ll need to obtain a special permit, known as a “ferry permit”, to fly the aircraft to the place of inspection. Both the 100-hour and annual inspections cover a similar scope, however, an aircraft owner may request to have the annual inspection replaced by a progressive inspection.


If you are carrying passengers or giving flight instructions for hire, the 100-hour inspection is necessary along with the annual inspection. However, it is not required if a student owns an aircraft and hires a certified flight instructor (CFI). Additionally, the A&P mechanic that carries out the 100-hour inspection does not need AI certification.


In other words, an annual inspection could be replaced by the 100-hour inspection, but the reverse shouldn’t happen.




While inspections play a crucial role in extending the lifecycle of an aircraft, without proper inspection and maintenance, aircraft can perform poorly and endanger the lives of the passengers on board. Parts always wear out, things need replacing and the airplane requires consistent servicing, otherwise, it could cause mid-flight problems. Inspections should be carried out according to the FAA regulations and the manufacturer’s recommendations.




The FAR 43, Appendix D dictates the scope and detail of what should be included in an annual and the 100-hour inspection. While the inspections carried out vary from plane to plane, here are the common items checked during a 100-hour inspection:



This is the electromechanical mechanism that develops the energy needed to make the engine rotate. The starter, along with the mounting bolts that secure it in place need to be checked over and secured. Additionally, watch out for other issues such as corrosion and electrical arcing. The starter’s teeth also need to be checked for any breakages.



The alternator belt needs to have the required tension and the condition of its surfaces also needs to be checked over for cracks, bumps and other wear-and-tear. The surfaces are accessed by rotating the belt between the pulleys one section at a time. The belt’s inner surface should be soft and supple – a hardened surface implies that the belt is damaged, and it will not be able to grip the mechanism as well as it should. If this occurs, it needs immediate replacement.



The alternator may require a slight movement of the belt’s tension if it’s not appropriately adjusted. Caution should be taken so as not to damage the alternator bearings.



While oil changes take place when aircraft undergo progressive inspections, the engine needs a thorough inspection of any other fluid, fuel, oil and hydraulic fluid leaks found during the 100-hour inspection.


All the drain plugs, fuel lines and fittings are checked for signs of leaking. The mechanic will be able to identify the leak’s source by switching on a boost pump, and while it’s running, inspect all the lines and fittings to pinpoint the source of the leak. Faulty parts require immediate replacement while loose fittings call for tightening.


Oil filters will be looked over, as well. Loose valve covers and dipstick joints could result in oil leaks, so they should not be loose. Keep in mind that excess torquing could cause brittle casings to crack, causing severe leaks; the aircraft flight manual (AFM) lets the mechanic know the proper torque that should be applied to your bolts.


The internal engine is susceptible to damages from foreign particles and is therefore subjected to inspection during the 100-hour inspection. The cowling also requires inspection for signs of cracks and other faults.


The inspection will uncover issues of improper installation of each engine component and certify that they are all in good working condition.




An A&P mechanic will evaluate the general well being of your aircraft by checking other items such as the windows, seats and safety belts, the condition of instruments and engine controls, batteries, and the fabric or skin condition.


Once the 100-hour inspection is finished, the aircraft owner should keep the inspection documents until the next inspection is due. While inspections are necessary to be in compliance with airworthiness rules and regulations, they also ensure passenger safety and keep the aircraft in optimum working condition. Something that every pilot can get behind.



Are you trying to keep your plane in perfect flying condition? Contact the professional team of mechanics at Citadel Aircraft Maintenance for all of your airplane inspection needs!



We service a wide variety of airplanes throughout the state of Minnesota and Midwest region, providing expert 100-hour plane inspections to those aircraft owners that never want to miss a day of flying. We provide top-tier inspection services that will leave you with peace of mind knowing your plane – and everyone aboard – is safe and sound.


The experience we offer gives pilots confidence in their aircraft and sets future expectations for a higher level of service. At Citadel  Aircraft Maintenance , we will always treat our clients’ planes like our own.


Get in touch with our team for a free quote on your aircraft’s maintenance needs.


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