An Air Carrier pilot flying an IMC AVL Runway 34 ILS reported a glide slope pitch up followed by a pitch down. The aircraft aggressively followed the ILS signal causing the crew to disconnect the autopilot and hand fly the aircraft to landing. The approach continued VMC but with a fluctuating glide slope signal.
Synopsis
An Air Carrier pilot flying an IMC AVL Runway 34 ILS reported a glide slope pitch up followed by a pitch down. The aircraft aggressively followed the ILS signal causing the crew to disconnect the autopilot and hand fly the aircraft to landing. The approach continued VMC but with a fluctuating glide slope signal.
Narrative
While on vectors to an AVL ILS Runway 34 we were given heading to intercept the localizer and cleared for the approach. The autopilot and flight director were engaged and the approach was followed per company profile. The glideslope was erratic and caused the flight director to capture too early and the airplane climbed 200 FT and then it nosed down approximately 5 degrees and entered a 2000 FT per minute descent. It was clear that the glideslope could not be followed and the autopilot was disconnected. Even when hand flying the glideslope could not be followed. We asked Tower and they said that it has had reported problems for 2 years and the FAA has flight tested the equipment and it was in tolerance. This glideslope does have a NOTAM Runway 34 COUPLED ILS APPROACHES BELOW 2960 NOT AUTHORIZED. WIE UNTIL UFN. CREATED: 04 FEB 19:58 2010. The glideslope was not usable while we were above 2960 and the glideslope was not usable while hand flying under 2960. Minor deviations were noted even when the aircraft maintained a constant descent. I don't believe the ILS should be used in IMC or at night. This should be a visual or LOC approach only.
NASA callback
The Reporter stated that at the time of the initial pitch up the aircraft was IMC and he would estimate the pull up G force was in excess of 1G followed by a .5G pitch down. The fluctuations continued until around 200' AGL. ATC responded to questioning about the Glide Slope stability and said an FAA Flight Check inspection found it within limits. The reporter has been flying into this airport for 6 years; has flown this specific aircraft many times and is certain that the issue is with the ILS. Because his aircraft's speed was relatively high the aircraft was maneuvering was well above a stall speed region; but if this pitch up occurred at a slower airspeed loss of control might result. He recalled that a similar event may have been part of the Buffalo DHC8 accident in which the aircraft was lost after an IMC pitch up.
More incidents for this aircraft family →
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.