<title>Field results of a high-reliability electromechanical display for the F-15 aircraft</title>

Abstract

Electromechanical flight instruments in military aircraft are being replaced by flat panels. One of the reasons often stated is to improve reliability. This paper discusses a project initiated several years ago to design, develop, qualify, manufacture and flight test an electromechanical Horizontal Situation Indicator (HSI) designed for high reliability for the F-15 aircraft. This indicator was to have a guaranteed Mean Time Between Failures (MTBF) of 10,000 hours minimum. This paper discuses the results of this project after completing development, qualification testing, manufacture and several years of operational flights on 2 squadrons of F-15 aircraft. The results will be compared to experience gained in flying flat panel displays in a commercial jet aircraft. The comparison shows that the electromechanical flight instrument as designed, demonstrates a reliability equal to or greatly exceeding that of current flat panel displays. Most electromechanical flight instruments in use today were designed and manufactured 25 to 30 years ago. Their intended useful life, by specification, was 10 years with an MTBF requirement of approximately 1,000 hours. It is shown that the specification requirements for useful life as well as reliability requirements can be greatly expanded for electromechanical flight instruments to equal or exceed that of flat panel displays. This paper describes some of the design techniques and test methods used which have achieved such high reliability of the electromechanical HSI in an F-15 environment. A case is thus presented for the continued application of high reliability electromechanical instruments in certain cockpit applications with many benefits to the user.