We can't see a flight where that would occur. The rudder failure took place only when the differential was 180 degrees or higher. Under even the most severe flying conditions, the temperature differential between the hydraulic fluid and the surrounding components never exceeds 90 degrees. That would leave the plane without navigational control if the primary rudder failed. But the tests showed that extreme temperature differences between the chilly outside atmosphere and piping-hot hydraulic fluid coursing through the backup rudder could cause the mechanism to fail. No jam was detected in either unit, he said. Once the full rudder hardover occurred, the flight crew was unable to counter the resulting roll with aileron because the B737 does not have sufficient lateral control authority to balance a full rudder input in certain areas of the flight envelope.Ĭharlie Higgins, a Boeing vice president who heads up airplane safety and performance for Boeing, said the rudder control units from the 737s in the Pittsburgh and Colorado Springs crashes were both thoroughly examined as a part of the NTSB's accident investigations. This secondary valve jam and primary valve overstroke caused USAir 427 to roll uncontrollably and dive into the ground. This deflection was a result of a main rudder power control unit (PCU) secondary valve jam which resulted in a primary valve overstroke. A contributing cause of this accident was the manufacturer's failure to advise operators that there was a speed below which the aircraft's lateral control authority was insufficient to counteract a full rudder deflection.".ĪLPA believes that the airplane experienced an uncommanded full rudder deflection. ![]() The NTSB, FAA, Boeing, US Airways and ALPA all had different opinions about the cause of these accidents:Īccording to US Airways the cause was: "An uncommanded, full rudder deflection or rudder reversal that placed the aircraft in a flight regime from which recovery was not possible using the known recovery procedures. Unfortunately none of the aircraft involved had modern, highly informative flight data recorders, so the NTSB staff were forced to make assumptions in developing its hypotheses. In 1996 the crew of an Eastwind Airlines flight 517 briefly lost control of their 737 as they approached Richmond, Va. The plane descended fast and impacted the ground nose first at 261kts in an 80deg nose down, 60deg left bank attitude and with significant sideslip. The left roll hesitated briefly, but continued and the nose again dropped. At 2000ft above the ground the aircraft's attitude passed 40deg nose low and 15deg left bank. The 737 continued to roll, but the nose began to rise. Left roll and yaw continued, and the aircraft rolled through inverted flight as the nose reached 90deg down, approx. At 19.03:07 the pitch attitude approached -20deg, the left bank increased to 70deg and the descent rate reached 3600f/min. The aircraft pitched down, continuing to roll through 55deg left bank. Within a second of the yaw onset the roll attitude suddenly began to increase to the left, reaching 30deg. ![]() ![]() At 19.03:01 the aircraft's heading slewed suddenly and dramatically to the left (full left rudder deflection). The airplane started rolling back to the right at an acceleration that peaked 36deg/sec, but the aircraft never reached a wings level attitude. Theğirst Officer then manually overrode the autopilot without disengaging it by putting in a large right-wheel command at a rate of 150deg/sec. The autopilot attempted to initiate a roll back to the right as the aircraft went in and out of a wake vortex core, resulting in two loud "thumps". Over the next 3 seconds the aircraft rolled left to approx. The aircraft then suddenly entered the wake vortex of a DeltaĚirlines Boeing 727 that preceded it by approx. At that moment the aircraft was levelling of at 6000ft (speedđ90kts) and rolling out of a 15deg left turn (roll rate 2deg/sec) with flaps at 1, the gear still retracted and autopilot and auto-throttle systems engaged. ![]() , US427, a 737-300 was approaching Pittsburgh Runway 28R when ATC reported traffic in the area, which was confirmed in sight by theğirst Officer. In that report, the NTSB said it “could not identify conclusive evidence to explain the loss of the aircraft”, but indicated that the two most likely explanations were a malfunction of the airplane’s directional control system or an encounter with an unusually severe atmospheric disturbance. After a 21-month investigation, the Board issued a report on the crash in December 1992. The aircraft departed from controlled flight approximately 1,000 feet above the ground and struck an open field. 3 March 1991, UA585, a 737-200Adv crashed on approach to Colorado Springs.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |