Comair B738 near Johannesburg on Mar 13th 2017, altitude deviation causes TCAS RA
Last Update: August 21, 2018 / 21:07:21 GMT/Zulu time
Incident Facts
Date of incident
Mar 13, 2017
Classification
Incident
Airline
Comair
Flight number
MN-6234
Departure
Port Elizabeth, South Africa
Destination
Johannesburg, South Africa
Aircraft Registration
ZS-ZWS
Aircraft Type
Boeing 737-800
ICAO Type Designator
B738
A SA Airlink Embraer ERJ-135, registration ZS-SNX performing flight 4Z-8053/SA-8053 (callsign LNK053) from Maseru (Lesotho) to Johannesburg (South Africa) with 16 passengers and 3 crew, was enroute at FL370 nearing their top of descent into Johannesburg when the crew received a TCAS Traffic Advisory. The captain, pilot flying, put his hands onto the flight controls in anticipation of a possible a Traffic Resolution Advisory, the crew looked out for the conflicting traffic indicated above them and established visual contact with the descending aircraft above and to their left, the crew concluded they were receiving the TCAS TA due to the high rate of descent by the other aircraft. Just at the same time the crew acquired visual contact a TCAS RA was issued. The aircraft maintained FL370 until TCAS announced "Clear of Conflict".
Both aircraft continued for safe landing.
South Africa's Civil Aviation Authority (SACAA) reported on Apr 21st 2017, that the two aircraft were on the same track towards waypoint IMGEV and OKTEC with the Boeing above the Embraer. The controller turned the Boeing left towards waypoint ETLIG. Shortly after the TCAS advisories activated. At about the time of the TCAS resolution advisory issued in the Boeing ATC queried the Boeing crew to confirm their flight level they were maintaining, the crew confirmed they were maintaining FL380, subsequently the crew announced they were following a resolution advisory (with the resolution advisory sounds audible during the transmission), upon another query by ATC about their maintained flight level the crew indicated they were still recovering from the resolution advisory. According to radar data the Boeing descended 560 feet below their assigned FL380 before recovering to FL380.
On Aug 21st 2018 the SACAA released their final report concluding the probable cause of the serious incident was:
After flight BA6234 was rerouted direct to ETLIG, the flight management computer required a faster descent rate in order to accomplish the planned vertical bearing for ETLIG. The crew began the descent from FL410 to FL380 but inadvertently (whether due to a human or machine error could not be established) descended through the assigned level before levelling off following a resolution advisory (RA).
The SACAA reported the minimum separation reduced to 500 feet vertical and 1.6nm horizontal. BA-6234 stopped the descent at FL375 and climbed back to FL380.
Incident Facts
Date of incident
Mar 13, 2017
Classification
Incident
Airline
Comair
Flight number
MN-6234
Departure
Port Elizabeth, South Africa
Destination
Johannesburg, South Africa
Aircraft Registration
ZS-ZWS
Aircraft Type
Boeing 737-800
ICAO Type Designator
B738
This article is published under license from Avherald.com. © of text by Avherald.com.
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