THE trend of engine failures of all types, in terms of number per 1,000,000 miles of operation or per 1000 aircraft licensed, has been rising steadily in both air-carrier and non-air-carrier operations, although a decline in frequency has been noted of late in the air-carrier group.
The principal increase in air-carrier operation has been due to an epidemic of spark-plug failures. The frequency of the remaining types of failures is noted to have been fairly constant in recent years. The same is generally true of structural engine failures in air-carrier service.
The most frequent type of failure in private operation is idling failure. However, idling failures do not entirely account for the increasing frequency of failure, since a rising trend is also noticeable in the number of difficulties exclusive of those in the idling category. Structural failures per unit number of aircraft in private operation also follow the same trend.