Page:NTSB Aircraft Accident Report, United Airlines Flight 389.pdf/27

 In addition to the above study, a review of Mechanical Reliability Reports on the B-727 was conducted to determine if there was any discernible trend in reports of static system problems or instrument problems traceable to the static system. No history of static systems or instrument problems was found.

Because of the failure of some of the speed brake actuators to pass a post-accident cold soak test, the history of spoiler malfunctions in the B-727 fleet was reviewed. It was found that when spoilers malfunctioned and the actuators would not pass a cold soak test, the problem appeared as a failure of some of the spoilers to extend when the speed brakes were selected to the extended position. This failure to extend resulted in unwanted rolling of the aircraft but was found to be controllable by the pilots. It was also noted that this problem only appeared at the high altitudes and was not reported at lower levels where an unwanted roll might be more hazardous.

As a part of this investigation a review of research on altimeter reading problems was conducted. There are some fifty studies relating to the various altimeter systems of presenting information to pilots which have been conducted since 1947. One of the most recent studies completed by the Naval Research Laboratory, Washington, D. C. was conducted to determine the relative effectiveness of various altimeter displays. These investigations, consisted of laboratory research at NRL and flight test at a nearby naval air facility, were in support of a Department of Defense program. Four types of altimeter presentations, the counter-pointer (CP), counter-drum-pointer (CDP), drum-pointer (DP) and three pointer (3P) were compared in a series of laboratory