INTRODUCTION

 One of the most important activities in promoting safety in aviation is the airworthiness certification of airplanes. Each airplane certificated by the Federal Aviation Administration (FAA) has been manufactured under rigid specifications of design, materials, workmanship, construction, and performance. This certification process provides adequate assurance that the airplane will not fail from a structural standpoint if the airplane is properly maintained and flown within the limitations clearly specified. However, this may not be true if the airplane is abused, improperly maintained, or flown without regard to its limitations.
 The goal of airplane designers and manufacturers is to obtain maximum efficiency, combined with adequate strength. Excessive strength requires additional weight which lowers the efficiency of the airplane by reducing its speed and the amount of useful load it can carry.

This chapter covers the airplane’s structure, flight control systems, wing flaps, landing gear, engine operation, engine accessories, and associated engine instruments. Also included is material related to aircraft documents, aircraft maintenance, and inspection procedures.

AIRPLANE STRUCTURE

 As stated in Chapter 1, Principles of Flight, the required structural strength is based on the intended use of the airplane. An airplane which is to be used for normal flying does not need the strength of an airplane which is intended to be used for acrobatic flight or other special purposes, some of which involve significant in-flight stresses.

 Numerous wing designs have been developed in an effort to determine the best type for a specific purpose. Basically, all wings are similar to those used by the Wright brothers and other pioneers. Modifications have been made, however, to increase lifting capacity, reduce drag, increase structural strength, and generally improve flight characteristics. Wing designs are subjected to thorough analysis before being approved for use on certificated airplanes. Strength tests determine the effect of strains and stresses which might be encountered in flight.

 Airplane strength is measured basically by the total load which the wings are capable of carrying without permanent damage to the wing structure. The load imposed upon the wings depends upon the type of flight in which the airplane is engaged. The wing must support not only the weight of the airplane, but the additional loads caused during certain flight maneuvers such as turns and pullouts from dives. Turbulent air also creates additional loads and these loads increase as the severity of the turbulence increases.

 To permit the utmost efficiency of construction without sacrificing safety, the FAA has established several categories of airplanes with minimum strength requirements for each. Limitations of each airplane are available to the pilot through markings on instruments, placards on instrument panels, operating limitations attached to Airworthiness Certificates, Aircraft Flight Manual, or Pilot’s Operating Handbook.

FLIGHT CONTROL SYSTEMS

 The flight control systems in most general aviation airplanes consist of the cockpit controls, cables, pulleys, and linkages connected to the movable control surfaces outside the airplane.
 There are three primary and two secondary flight control systems. The primary flight control systems consist of the elevator, aileron, and rudder, which are essential in controlling the aircraft. The secondary control systems consist of the trim tabs and wing flaps. The trim tabs enable the pilot to trim out control pressures, and the flaps enable the pilot to change the lifting characteristics of the wing and also to decrease the speed at which the wing stalls. All of the flight control systems, except the wing flaps, were discussed in Chapter 1, Principles of Flight. The flaps will be discussed at this point.