REPORT###REPORT###
jet2.com B733 at Chambery on Feb 7th 2010, EGPWS alert during ILS approach
A jet2.com Boeing 737-300, registration G-CELC performing flight LS-451 from Leeds,EN (UK) to Chambery (France) with 103 passengers and 6 crew, was on approach to Chambery with the intention to perform an ILS approach to runway 18 but circle to land on runway 36. The first officer was pilot flying. The aircraft passed the initial approach fix when ATC advised the crew that winds were from 360 degrees at 7 knots and asked whether the crew could accept a landing on runway 18. The captain replied that if the wind remained the same they could. The aircraft was then cleared for the approach. The aircraft left the hold at the initial approach fix at an altitude of 6500 feet in instrument meteorologic conditions and proceeded according to the published approach procedure with the autopilot engaged. After the CY VOR had been selected for most of the approach the captain selected CY ILS and found it indicating normally indicating a DME of 13nm. At DME 12 at an altitude of 5000 feet the autopilot captured the localizer, at DME 11 the VS mode of the autopilot activated and the aircraft began to descend at 2200 fpm. The captain noticed the loss of ILS information on his electronic attitude indicator (EADI) and looked across to see whether the first officer's indications were still there. They appeared to be, so he looked down at the AUTO/MAN selection switch for the navigation frequency to determine whether the correct frequency was set, recycled the switch and the ILS indications returned to view. ATC contacted the aircraft with a frequency change instruction, the captain acknowledged, but before he completed the frequency change he noticed that the airplane was below the glideslope and descending in excess of 2000 fpm. The commander queried the first officer "are you happy", the first officer replied he was not and initiated a go-around. At that time an EGPWS "TERRAIN TERRAIN PULL UP" alert activated. The captain called positive climb, the gear was selected up, and the aircraft climbed through 6000 feet at an pitch angle in excess of 20 degrees nose up and 110 KIAS. The first officer lowered the nose to accelerate, the crew set course for the CY NDB being uncertain of their position and the reliability of their other navigation systems. The captain queried ATC about the serviceability of the ILS and was assured the ILS was serviceable. The crew subsequently performed a second approach and completed a safe landing.
The AAIB released their bulletin reporting that the operator had provided a comprehensive brief for Chambery including the note: "Beware of possible false glide-path indications. The glide path should not be used until within 12.1 DME CY."
THe airplane had a flight management system installed without GPS. An EGPWS was installed which provided its own GPS source. The GLIDESLOPE alert is active below 1000 feet radar altitude and with the landing gear extended.
Usually an ILS approach is being flown with the autopilot in approach mode, however, if a circling is to follow the ILS approach, the manufacturer recommends to use the VOR/LOC (lateral) and VS (vertical) modes. The operator had adopted this recommendation as standard operating procedure.
The investigation had a complete recording of the flight data recorder and the EGPWS recording of the terrain alert, however the cockpit voice recorder capable of storing 2 hours had been overwritten during the return flight.
The flight data recorder showed that the airplane had levelled at 5000 feet with the autopilot in ALT and VOR/LOC mode. The autopilot captured the localizer from the right doing a gentle turn. At 11DME the vertical channel was changed to VS, at that point the airplane was about 850 feet below the glideslope, the airplane started to descend at 2200 fpm. About 10 seconds later the captain's localizer and glideslope were briefly shown not computed indicating the raw data were no longer available or not reliable, the DME showed 10.5nm which was accurate. During the further descend the captain's localizer and glideslope were shown not computed two more brief times.
The airplane was approaching the airport from the north requiring the aircraft to fly over the ridge of high ground to the east of Lake Bourget. As the airplane descended the terrain closure rate progressively increased to 6000 fpm. When the airplane descended through 1125 feet the EGPWS level 2 terrain alert activated. At the same time the autopilot was disengaged and a go-around was initiated - due to recording rates it could not be determined whether the go-around was initiated prior to or after the EGPWS alert. The minimum terrain clearance was 1112 feet. The aircraft reached a maximum nose up attitude of 32.7 degrees shortly after the EGPWS alert, the minimum airspeed was 109 KIAS, the aircraft stabilized at a climb rate of 3800 fpm.
During the subsequent approach and landing no further anomalies were recorded in the localizer, glideslope and DME data.
The first officer reported in post flight interviews, that the aircraft had intercepted the localizer satisfactority however he had noticed the DME on the ILS was intermittent. Flaps 15 were selected and the gear was extended. He saw the glideslope pointer rapidly move down the scale and in response selected VS and selected a descent rate he intended to be 1200 fpm. He recollected that the captain remarked "it's operating in the reverse sense", he took it to mean the localizer indication. He expanded his VOR/ILS display and observed the beam bar was slightly offset. The first officer commented that this action briefly distracted him from monitoring the descent profile.
The first officer recalled that he caught a glimpse of a mountain through a gap in the cloud, noticed that the airplane was way below the glideslope at a high rate of descent, he heard the commander say "are you happy" and disconnected the autopilot and commenced a manual go-around without selecting TOGA as he thought they were above 2000 feet with TOGA being unavailable. When he heard the EGPWS he increased the pitch angle to as much as possible. After the airplane climbed clear of the cloud he levelled to accelerate before continuing to climb to FL090. He commented that the control column needed a strong push to recover the airplane to level flight.
The captain said in post flight interviews that the landing runway was to be deicided once visual contact was established. After selecting the ILS frequency he saw the airplane was established on the localizer though slow in acquiring the center line, he called "12 DME with descent at 8.9" aiming to remind the first officer about the descent point. After passing 11.7 DME his ILS indications were gone and ILS fail flags appeared in view, there was no DME indication. He checked the first officers instruments where the indications were still present. He then recycled the AUTO/MAN switch after which the ILS and DME indications re-appeared. His attention then returned to the flight instruments and he recalled the airplane was descending at a high rate and was below the glideslope. He questioned the first officer who in turn initated a go-around.
The AAIB analysed that there was no evidence of any signal interruption or failure on the CY ILS or DME. The aircraft's navigational equipment was found serviceable when tested after landing. The reason for the first loss of the commander's localizer, glideslope and DME indication could not be determined. However, the second and third period of "not computed" signals were probably the captain's actions to recycle the AUTO/MAN switch.
While the commander's attention was diverted to the ILS display problem the first officer initiated a descent at an excessive rate before the aircraft had reached the final approach fix. The commander remained unaware of that descent profile until his attention returned to monitoring the flight profile, he questioned the situation, the discrepancy was acknowledged and the first officer initiated a go-around. The terrain clearance never reduced below 1100 feet.
