Etihad B78X at Abu Dhabi on Jun 6th 2020, descended below vertical profile on short final
Last Update: October 12, 2021 / 15:38:09 GMT/Zulu time
Date of incident
Jun 6, 2020
Abu Dhabi, United Arab Emirates
Boeing 787-10 Dreamliner
ICAO Type Designator
Airport ICAO Code
The United Arab Emirates GCC released their final report into the serious incident concluding the probable causes were:
The Air Accident Investigation Sector determines that the cause of the Aircraft flying below the vertical profile during approach was the incorrect local pressure (QNH) altimeter setting. A Go-around was carried out when the Aircraft was at a distance of 1.3 nautical miles from the threshold of runway 31L after the flight crew had definitely seen four red precision approach path indicator (PAPI) lights.
The Air Accident Investigation Sector identifies the following contributing factors to the Incident:
- The operating flight crew omitted to preset QNH value after receiving automatic terminal information service (ATIS) information, even though the Commander had confirmed to ATC that EY9878 had received ATIS Information India which contained OMAA QNH 999 hPa.
- Prior to and at transition level, the flight crew were fixated on the high-energy management for the descent, such that selecting the barometric setting from the standard pressure of 1013 hPa to the local QNH value was carried out incorrectly.
- ATC did not provide the OMAA QNH information along with the initial descent clearance from a flight level to an altitude, nor when issued the clearance of RNAV Y runway 31L approach from IAF.
- The VSD and its cues were not used or considered of their vertical profile assessment during approach by the flight crew for monitoring.
- ATC did not provide instruction to check the QNH setting and the level of the Aircraft when the activation of the minimum safe altitude warning was triggered on its radar screen.
- At higher altitudes, the forward visibility was less than reported, due to the presence of haze layer(s) of which are commonly associated with temperature inversions in the Middle Eastern region.
The GCAA analysed that the aircraft was high on the standard arrival route and needed to extend the speed brakes, the crew changed from VNAV to FLCH twice to accomplish the descent. The GCAA continued:
As mentioned before, VNAV PTH was activated when the Aircraft was descending crossing 2,150 feet indicated altitude.
Prior to passing KUSOK, the flight crew ended the communication with Approach Control as instructed to contact Tower Control. Up to this point, the QNH information had never been provided by the Approach Control.
The aircraft was subsequently configured for landing with flaps 25 at Vapp 148 KIAS, after passing KUSOK the flight mode was VNAV PTH. The GCAA stated:
When the Aircraft was descending through 1,610 feet indicated altitude, the speedbrakes were retracted. The airspeed reached 151 knots, and the Aircraft was on the indicated profile. Since a baro-VNAV approach was being flown with an incorrect QNH setting, the Aircraft flew below the nominal profile. The flight crew perceived the indicated profile as the correct vertical profile, and were, most probably, released from their concern of being high, with a correct airspeed.
The Aircraft was descending through 1,390 feet indicated altitude. The outside air temperature was approximately 39 degrees Celsius, or in a standard atmosphere, the actual atmosphere was at ISA+27 condition.
The Commander stated that he checked the altimeter immediately when the auto callout of 1,000 feet was annunciated, however, he could not recollect the precise number of the indicated altitude. At 1,000 feet radio altitude, the indicated altitude showed around 1,350 feet, and the distance was approximately four nautical miles as per the flight data. The Copilot also stated that he heard the “1,000” auto callout. The SOP required the pilot monitoring to crosscheck the distance to touchdown in response to “1,000” radio callout. The Copilot as the pilot flying might have crosschecked that the Aircraft was on profile (with the incorrect QNH setting).
Since the flight crew perceived the indicated profile as the correct vertical profile, hence, the Commander as the PM, most probably, did not consider the need to crosscheck further the vertical situation of the Aircraft for the remainder approach. Should the Commander have crosschecked correctly the distance to the runway threshold that indicated approximately four nautical miles, in response to the “1,000” auto callout, he would have probably realized that the Aircraft was below the nominal vertical profile. And in that case, he might have commanded the Copilot to perform an earlier go-around and could have prevented the occurrence as the last barrier. Therefore, the Investigation believes that pilot’s response after the “1,000” auto callout was not effectively managed as per the SOP. However, the Investigation could not determine whether the required callouts in response to “1,000” auto callout was made by both flight crew since the CVR data was unavailable.
The Aircraft descended passing 500 feet radio altitude while the indicated altitude showed 865 feet. The autopilot was disengaged when the Aircraft passed 660 feet indicated altitude (280 feet radio altitude), at which point manual flight was first applied.
The takeoff/go-around (TOGA) mode was engaged with the simultaneous engagement of the autopilot when the Aircraft was at a distance of approximately 1.3 nautical miles from the threshold of runway 31L. The indicated altitude was 570 feet and the radio altitude was around 210 feet.
The Copilot, as the PF, did not call for a go-around when he became aware of the vertical profile anomaly as he saw the four red PAPI lights.
The Commander, as the PM, stated that he saw the four red PAPI lights, and realized that something was not right, hence, he instructed the Copilot to go around. The PF then initiated the go-around by pressing the TO/GA switches.
The Investigation could not determine the precise time when the go-around order was made by the Commander since the CVR data was unavailable. However, based on all three flight crewmembers, none of them raised a concern that there was a delay between the time the Commander ordered the go-around and the commencement of the go-around.
Therefore, it can be considered that the go-around was performed immediately after the order to go-around was made. The TO/GA switch was pressed when the Aircraft was approximately 1.3 nautical miles. Hence, it can be considered that the Commander saw the four red PAPI lights, and instructed the Copilot to go around when the Aircraft was approximately 1.5 nautical miles from the threshold.
The GCAA continued analysis of the go around:
While the Aircraft was turning right from crosswind leg to downwind leg at a level of 4,000 feet indicated altitude as per the vectors provided, the Approach Controller requested confirmation that the flight crew had established the QNH setting of 998, and queried the flight crew about the present altitude, which was not a standard ATC request addressed to the flight crew. This indicates that the Controller was not certain of the QNH setting in the Aircraft since 3,700 feet was shown on the ATC’s display.
Consequently, the flight crew realized that they had the incorrect QNH setting on their primary flight displays (PFD). The true altitude was 300 feet below the indicated altitude in the flight deck, and it was identical to the ATC display. Subsequently, the flight crew adjusted the altimeter settings to 998 hPa and informed the Controller that the Aircraft would climb to 4,000 feet.
The GCAA analysed the ATC performance:
As described previously, when the Aircraft was at a distance of approximately three nautical miles prior to reaching EMERU waypoint, Abu Dhabi Approach Control instructed the flight crew to descend to 7,000 feet and cleared for an RNAV Y approach to runway 31L from TUGVA (IAF). The instruction ‘to descend to 7,000 feet’ was an initial descent clearance to an altitude without providing the local QNH information, which was not in accordance with the air traffic services operating manual (ATSOM).
Also, when the RNAV Y approach to runway 31L from TUGVA clearance was provided, the Controller did not provide the local QNH information, which was not in accordance with the Supplementary Instruction (SI) 027/20 that had been issued by the air traffic services (ATS) unit on 10 May 2020. This SI 027/20 required the controller, for OMAA arrivals, to provide the QNH information in the clearance of ‘RNAV YANKEE Approach’.
The Controller did not provide verbally the local QNH when the initial descent clearance to an altitude of 7,000 feet, and RNAV Y approach to runway 31L from TUGVA clearance were provided, since the flight crew had confirmed receiving ATIS information India that contained the QNH value of 999 hPa on the first contact with Abu Dhabi Approach Control.
The GCAA analysed the time of notification of the serious incident:
The Incident was notified to the Air Accident Investigation Sector of the United Arab Emirates (AAIS) about 23 hours after its occurrence. Before the notification, the Aircraft was being operated as per the flight schedule. The AAIS Duty Investigator requested the Operator to remove and preserve one of the recorders. The Operator had translated the requirements of notifying or reporting a serious incident in its OM-A.
The requirements mentioned that the commanders involved must take action to notify when they believe a potentially serious incident has been involved. In this Incident, the Commander did not start the communication procedure required.
As discussed in section 2.2 of this Report, the flight crew were not aware that the Aircraft was about 200 feet above the ground level when the go-around was performed. The flight crew did not appreciate the severity of the event of seeing the four red PAPI lights. The seriousness of the event was only appreciated after the Commander’s air safety report (ASR) and flight data monitoring (FDM) information was reviewed. Since the Aircraft did not experience any airworthiness issues after the Incident flight, therefore it was used on its next scheduled service. The flight crews’ lack of appreciation of the occurrence severity, precluded them from reporting this to the necessary personal in the Operator’s organization, and therefore, the Operator could not take the necessary steps to secure the CVR earlier. Since the CVR had only two hours of recording capability, the recorded data from the Incident flight had been overwritten.
The flight data recorder (FDR) had a recording capability of 72 hours. Therefore, the flight data for the Incident flight was available and was useful to the Investigation.
OMAA 060900Z 30006KT 260V340 CAVOK 41/23 Q0999 NOSIG
OMAA 061000Z 30010KT CAVOK 42/21 Q0998 NOSIG
Date of incident
Jun 6, 2020
Abu Dhabi, United Arab Emirates
Boeing 787-10 Dreamliner
ICAO Type Designator
Airport ICAO Code
This article is published under license from Avherald.com. © of text by Avherald.com.
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