A Ryanair Boeing 737-800, registration EI-EMK performing FR-8592 from London Stansted,EN (UK) to Bergerac (France) with 166 passengers and 6 crew, was on NDB approach Y to Bergerac's runway 28 in instrument meteorological conditions, when the aircraft descended below minimum safe altitude at about the time the aircraft was handed off to tower. At about the same time the approach controller received a Minimum Safe Altitude Warning and the aircraft's EGPWS issued a warning. The crew initiated a go-around and climbed to safe altitude, then positioned for another approach and landed safely on runway 28 about 24 minutes after aborting the first approach.
The French BEA reported in their weekly bulletin that the occurrence was rated an incident and is being investigated by the BEA.
On Jun 26th 2020 the BEA released their final report in French (Editorial note: to serve the purpose of global prevention of the repeat of causes leading to an occurrence an additional timely release of all occurrence reports in the only world spanning aviation language English would be necessary, a French only release does not achieve this purpose as set by ICAO annex 13 and just forces many aviators to waste much more time and effort each in trying to understand the circumstances leading to the occurrence. Aviators operating internationally are required to read/speak English besides their local language, investigators need to be able to read/write/speak English to communicate with their counterparts all around the globe).
On Sep 7th 2020 the BEA also released their English translation of the final report /(editorial note: the following summary is based on the French report translated by The Aviation Herald in June 2020).
The report concludes the probable causes of the incident were:
The incident occurred while the aircraft performed an NDB approach without DME, probably without external visual references.
The first preparation of the approach was probably incomplete or imprecise.
Thus, the clearance by ATC although concerning the approach procedure the crew believed they had prepared, seemed to have put their prepared actions into question and required re-programming of the FMS.
This late modification did not permit the crew to agree on the guidance modes to be used. This resulted in confusion of the captain as to the horizontal trajectory to be followed by the aircraft. Confronted with these doubts, rather than opting for waiting circuit or return to basic control of the aircraft, this state of confusion led him to request an early descent below the safety altitude.
Contributing factors were:
- concerns by the captain, in particular related to extreme noise pollution in his headset and his doubts about the involvement of the first officer
- the first officer's weak experience with this type of approach which caused at the very least the failure to detect inconsistencies of the instructions issued by the captain
The following factors contributed to the descent below minimum safe altitude for nearly two minutes until the EGPWS alerted "TERRAIN! TERRAIN!" as well as the triggering of the controller's minimum safe altitude warning:
- the greatly reduced situational awareness of both pilots
- the ATC controllers lack of monitoring of the aircraft's trajectory ignoring the NDB procedures
- the absence of an altitude alert system at Bergerac Airport (or its remote control) and failing this the lack of urgent coordination procedures between Bergerac and Aquitane Approach Control in case of a minimum safe altitude warning
The BEA reported the aircraft was on approach to Bergerac cleared to descend to FL070 when the controller (Aquitane Approach) queried whether they wanted to perform an RNAV approach, the first officer answered "No ... Yes" and requested the weather conditions at the aerodrome. The controller subsequently queried again whether they wanted to perform an RNAV approach, this time the first officer answered they wanted to perform an NDB approach, the controller advised to expect the NDB Y approach for runway 28, cleared them direct to the NDB BGC and cleared them to descend to 2500 feet MSL. The aircraft overflew the NDB at 2723 feet MSL with the autopilot modes LNAV and V/S active. The autopilot subsequently levelled the aircraft off at 2500 feet and 185 KIAS, 3 seconds later the crew extended the flaps to 5 degrees. While the aircraft initiated a left turn on LNAV, the first officer selected a vertical speed of -900 fpm, later -1200 fpm and a target altitude of 900 feet and again descreased the rated of descent gradually to 300 fpm. The aircraft rolled into another left turn at 1447 feet MSL and 175 KIAS, the crew radioed they were established inbound, the aircraft however was 65 degrees off the final approach course at that point. Approach control handed the aircraft off to Bergerac tower.
While the crew is changing frequency to Bergerac Tower, without yet communication with the tower and no longer communicating with approach, the approach controller received a minimum safe altitude warning for the aircraft. Several seconds later the crew contacted tower at 1240 feet MSL and were cleared to continue the approach.
24 seconds after establishing radio contact with tower the crew received an EGPWS alert "Terrain! Terrain!", more than 8nm from the runway threshold, still in the left turn at 1054 feet MSL and 842 feet AGL, the autopilot was tracking modes LNAV and ALT ACQ. 2 seconds later the TOGA button is pressed at 1018 feet MSL, 797 feet AGL, 164 KIAS and -986 fpm. At the same time EGPWS sounded "Pull Up!"
A second minimum safe altitude warning activated on the approach controller's desk. The crew announced on tower frequency they were going around, the aircraft climbed to 4000 feet MSL, contacted approach again and position for another NDB Y approach to runway 28, which was without further event. The aircraft landed safely.
The BEA analysed, that the ILS and DME were not available on the day of the occurrence due to maintenance works. The captain consulted with the booklet provided by the operator and found no mention of the RNAV/GNSS approach procedures and concluded the procedures were not permitted by the operator. Therefore the crew performed a briefing for the NDB approach near the top of descent. The captain considered that the NDB procedure was appropriate but did not specify whether he wanted NDB Z or NDB Y. The controller advised NDB Y approach, which required the first officer to reprogram the FMS. The results of the reprogramming did not satisfy the captain, who then announced he would fly the approach in HDG and V/S autopilot modes. He remained unaware of the first officer's lack of experience with this type of approach, after passing BGC LNAV and V/S modes were engaged. The aircraft turned to join a distant track consistent with entering the hold at BGC with a direct entry. The autopilot initiated a second left turn again consistent with a hold pattern rather than joining the final approach course.
In this turn the captain requested the first officer to descend, the first officer initiate a descent to 900 feet MSL at 900 fpm, then 1200 fpm. This descent below the minimum safe sector altitude as well as the descent before being aligned with the runway extended center line led the aircraft to leave the procedurally protected airspace and descend below minimum safe sector as well as below the procedural altitude.
While still in the turn the captain probably detected an anomaly and instructed the first officer to reduce the descent. The first officer reduced the rate of descent to 300 fpm, which exposed a fault, when the ALT ACQ mode activated the rate of descent automatically increased again leading to the EGPWS "Terrain! Terrain!" alert. The first officer aborted the approach, at the same time the EGPWS "Pull Up!" alert activated. The aircraft had been below minimum safe altitudes for nearly 2 minutes in instrument meteorologic conditions, probably without external visual references.
The BEA analysed that the first officer believed he had programmed the NDB Y procedure (the investigation did not determine whether NDB Y or NDB Z were present in the database and were programmed), following the ATC instructions he needed to reprogram the approach procedure which seems to indicate the approach procedure NDB Y was either not initially selected or had been selected incorrectly. NDB Z required the use of the DME, which was not available.
The LNAV mode was contrary to the instruction by the captain, who instructed to use HDG and V/S modes.
The target altitude of 900 feet MSL corresponded to the MDA rounded up to the next 100 feet.