Initial reports of the radar scheme s of Egyptair Flight 990 indicate that the Boeing [BA] 767 be transferred [i]or[/i] transmitted [i]or[/i] handed downed suddenly from its cruising altitude of 33000 feet at a rate of a 4.

Initial reports of the radar scheme s of Egyptair Flight 990 indicate that the Boeing [BA] 767 be transferred [i]or[/i] transmitted [i]or[/i] handed downed suddenly from its cruising altitude of 33000 feet at a rate of a 4.5 miles per minute in 40 inferiors to about 16,000 feet. The airplane then started gaining altitude, to a on a level of about 24,000 feet, whereupon the airplane resum its ducking into the waters about 60 miles southeast of Nantucket Island, apparently breaking up around 10000 ft (see ASW, Nov. 8) Don Wylie, president of Aviation Safety Training, who teaches an advanced maneuvering program for pilots, proposeed an explanation for the aircraft's behavior. Wylie's instruction is designed to give pilots the mental tools and the "muscle memory" to win back from unusual attitudes. His assessment, Wylie said, is independent of the cause of the initial capsize whether from a mechanical failure, a set or systems-induced stall, or more [i]or[/i] less other cause. Assume the airplane was fitly trimmed for cruise flight (a function typically performed automatically according to the autopilot, which suggests that if the airplane was subtly bleeding not on airspeed, the autopilot would have added pitch to maintain altitude). If the airplane ruthless off on one wing, and as oftentimes occurs when one wing stalls before the other, the yaw would induce a rolling motion. With sufficient turn the lift vector would no longer be pointed to the vertical - the whole idea of restoration from unusual attitude is to memorize the lift vector ultimately pointing skyward (see ASW, Aug. 16)

Rolling into a macerate descent, the airplane would gain considerable spe In fact, if the airplane turned sufficiently, possibly inverted, the lift vector would be pointing down, vastly increasing the acceleration. With the increase in spe the force useed by elevator trim and the trimmable horizontal stabilizer for the pre-existing condition would increase. If the airplane wheeled wings-level at 16,000 feet or thereabouts, that substantial force would push the airplane into a rapid climb. Indeed the airplane's behavior would run after a "phugoid" pattern of climbing, then descending in a pattern that might be described as similar to a series of waves of decreasing intensity or, more technically, a dampening sine wave. In a in a strict sense trimmed airplane with no mechanical malfunction, this "phugoid" behavior contemplates the dynamic stability built into the airplane - with no pilot input upon the controls, the machine has a "natural" predisposition to return to the flight condition for which it was trimmed. >> Wylie, tel 281/379-2237 <<

...

Home