Luxair E145 at Madrid on Aug 4th 2011, EGPWS terrain alert
Last Update: April 18, 2013 / 16:34:23 GMT/Zulu time
The incident occurred because the aircraft descended below the minimum standard terminal arrival route, minimum radar vectoring and minimum sector altitudes. The crew, which was obligated to maintain separation with terrain and know that the minimum altitude specified by the arrival procedure was 10,000 ft, descended below said altitude without confirming with ATC whether the clearance given was correct.
The RES sector controller used improper phraseology and cleared the aircraft to descend to 10,000 ft. The crew acknowledged descending to 5,000 ft and the controller did not correct the faulty readback. Also contributing to the incident is the fact that the RES and AIS sector controllers did not notice that the aircraft had descended below the minimum altitude in the procedure and below the minimum radar vectoring altitude. The AIS sector controller only realized this fact after being informed by the crew when the aircraftÂ’s EGPWS alerted them and they started to climb.
The aircraft was approaching Madrid's Barajas Airport, approach control had advised the crew to expect runway 18L for landing and cleared the flight to FL140 before handing the flight off to the direct east sector (RES). Upon reporting on that frequency the controller cleared the flight to continue descent to "tenthousand feet QNH 1016", the crew read back descending to fivethousand feet 1016, which was not challenged by the controller.
Two minutes after that transmission a shift change occurred, the controller was relieved, the incoming controller noticed the flight was still above 10,000 feet and above approach minimum (10,000 feet) and radar vectoring minimum (9,000 feet). Another 4 minutes later, when the aircraft was about to be handed off to the next arrival sector, the aircraft had descended to 7676 feet MSL below approach minimum (still 10k) and radar vectoring minimum (still 9k), the aircraft was handed off to the next frequency. When the crew reported on that frequency, already at 7349 feet, stating "descending to 5000 feet", the controller cleared the aircraft to "RADAR CONTACT MAINTAIN HEADING AFTER TAGOM FOR RUNWAY 18L".
The aircraft continued to descend below minimum sector altitude until the crew received EGPWS alerts "TERRAIN! TERRAIN!" and "TERRAIN! PULL UP!" The crew disengaged the autopilot and started the climb, the aircraft reached its lowest point at 6290 feet MSL. The crew advised they would be maintaining 7000 feet due to a mountain, the controller now instructed the crew to climb back to assigned 10,000 feet.
The CIAIAC reported the first officer (29, CPL, 2,279 hours total, 2,050 hours on type) was pilot flying, the captain (42, ATPL, 6,825 hours total, 3,988 hours total) was pilot monitoring. The captain had flown in Barajas the day before when it was in a south configuration different to the incident day.
The CIAIAC analysed: "The RES sector controller did not detect the faulty readback. The RES sector controller subsequently transferred the aircraft to sector AIS while it was descending and already below the minimum altitude specified in the procedure and below the minimum vectoring altitude, without either controller noticing it, either from the information on the radar screen or from the communications with the aircraft when its crew reported to the AIS sector controller that it was descending to 5,000 ft. The aircraft was below the minimum altitude in the procedure for about four minutes, and below the minimum vectoring altitude for below three minutes without the RES or AIS sector controllers or the crew itself noticing this. Once the EGPWS issued an alert, the crew acted in accordance with the procedures in its Operations Manual, disengaging the autopilot and initiating a climb."
The CIAIAC went on to analyse that the instruction to descend to "tenthousand feet" had not been in compliance with standard phraseology that would have required to say "one zero thousand feet". Eurocontrol recommends for altitude clearances issued between 10,000 and 11,000 feet to state: "Altitude one one thousand feet, that is eleventhousand feet" or "Flight Level one zero zero, that is one hundred".
With respect to the crew actions the CIAIAC analysed: "The crew acknowledged 5,000 ft even though the approach charts specified a minimum altitude for the procedure they were flying of 10,000 ft. Item 184.108.40.206 of SpainÂ’s Air Traffic Rules states that the pilot must ensure that any clearance issued by ATC is safe from the standpoint of preventing collisions with terrain except when a direct route is provided that takes the aircraft off an established ATS route. Moreover, as per 220.127.116.11 of the Air Traffic Rules, when an aircraft making a standard approach is cleared to descend to a flight level lower than the level(s) specified in the standard procedure, the aircraft shall follow the vertical profile published in the procedure unless ATC explicitly cancels those restrictions. Published minimum levels based on terrain clearance shall always be applied."
With respect to ATC performance the CIAIAC analysed that the false readback was not detected by the outgoing RES controller, the descent below assigned altitude and minimum radar vectoring altitude was not detected by the incoming controller and the controller of the subsequent sector even though the crew again reported to descend to 5000 feet, however, neither controller detected the error and the fact that the aircraft had descended below safe altitudes until the crew advised they were climbing due to a mountain. The CIAIAC stated: "Also worth considering is the fact that the aircraftÂ’s path and position were shown on the radar screens at the different controller stations and that there are two controllers at each post in the approach control sectors: an executive controller and a planning controller. Neither of them noticed that the aircraft was descending below the minimum specified in the approach procedure or below the minimum radar vectoring altitude. It is important for ATC personnel to remain vigilant at all times regarding the information displayed on the radar screen (aircraft labels) so as to detect possible deviations by the aircraft from the clearances issued by ATC or from established procedures, particularly when transferring an aircraft or when contacting an aircraft for the first time and reporting radar contact."
Three safety recommendations were released as result of the investigation.
This article is published under license from Avherald.com. © of text by Avherald.com.
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