A Study of Flap Management, an Analysis of the Consequences of Flap Management, and a Search for Possible Causes

Abstract

An exploration of current aviation education as to the purpose, aerodynamic theory, and proper usage of high lift devices, particularly trailing-edge 'wing flaps, was conducted. Aircraft accident data involving the mismanagement of the wing flaps as a cause/factor were analyzed and typical accidents were studied. The accident data show that a relatively high number of flap-related accidents occur and with dangerous consequences. Flight tests were conducted to recreate certain conditions of flight reported in the accident data. T~e following paper presents an in-depth explanation of the purpose, the aerodynamic theory, and the aircraft performance related to the proper usage of wing flaps. Additional data relative to the dangers of flight safety associated with the incorrect use of wing flaps is included. This study was primarily concerned with single-engine and twin-engine airplanes used for flight training. INTRODUCTION During the preparation of lectures for a course in basic aerodynamics, a number of aviation textbooks and flight manuals were studied for material concerning the management of wing flaps. It was observed that there is no consistency in how the various aspects of wing flaps are explained. In some flight training manuals and textbooks, there are statements of the purpose of flaps and descriptions of the different types of flaps available, while in other textbooks there are explanations of the changes in the coefficients of lift and drag caused by the extension and retraction of wing flaps. In pilot operating handbooks, instructions for the use of flaps are brief statements of what amount of flaps to use for takeoffs and landings. However, these handbooks generally do not explain the reasons for a particular flap setting or restriction. As a consequence, an investigation was begun of the purpose of wing flaps, the aerodynamic theory of wing flaps, the procedures for the use of wing flaps, and the reports of flap-related accidents. A review of the National Transportation Safety Board (NTSB) Briefs of Accidents for a six-year period showed that, on an average, one flap-related accident occurred every 9.4 days, injuring three persons, one, fatally. To investigate more the mismanagement of flaps, specifically during a go-around, flight tests were conducted duplicating certain accident conditions. METHOD A review of related literature was conducted for material concerning: (a) aerodynamics theory related to wing flaps; (b) the purpose of high lift devices, particularly trailing edge wing flaps; (c) types of high lift devices; (d) the procedures for the use of wing flaps; and (e) flap management and the dangers of mismanagement. The NTSB Briefs of Accidents were analyzed to determine: (a) the types of flight operations involved and the number of accidents which occurred during each of these phases of flight, (b) the number of accidents that were training related, and (c) the number of types and injuries involved. In addition, each category of 10 1 Kluga: A Study of Flap Management, an Analysis of the Consequences of Fl Published by ERAU Scholarly Commons, 1991 accidents was analyzed and the aspect of flap mismanagement involved was discussed. Aircraft performance data for a generic, single-engine airplane in the clean and flaps-down configurations were computergenerated to show the impact of wing flaps on aircraft performance. In addition, flight tests were conducted in a Cessna 172N to document go-around performance at different flap settings. REVIEW OF RELATED LITERATURE A review of literature related to single-engine and twin-engine aircraft used for flight training was conducted for material concerning aerodynamic theory, the purpose of high lift devices, types of high lift devices, procedures for the use of flaps, and flap management.