Jet Airways B773 over Turkey on Aug 8th 2014, loss of altitude

Last Update: December 28, 2015 / 14:31:14 GMT/Zulu time

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Incident Facts

Date of incident
Aug 8, 2014

Classification
Report

Airline
Jet Airways

Flight number
9W-228

Departure
Mumbai, India

Destination
Brussels, Belgium

Aircraft Registration
VT-JEL

Aircraft Type
Boeing 777-300

ICAO Type Designator
B773

A Jet Airways Boeing 777-300, registration VT-JEL performing flight 9W-228 (dep Aug 7th) from Mumbai (India) to Brussels (Belgium), was enroute at FL340 over Turkey crossing waypoint CRM (Position N41.265 E36.548). The captain (40, ATPL, 12,845 hours total, 4,785 hours on type) was taking a controlled rest and was asleep, the first officer (46, CPL, 7,388 hours total, 4,332 hours on type) was in control of the aircraft, autopilot and autothrust were engaged. Over CRM the aircraft performed a turn, the first officer intended to adjust the heading bug to the new heading 292, however, inadvertently adjusted the altitude window and activated the altitude FL292 sending the aircraft into a descent. Turkish Area Control Center noticed the descent and queried the flight, at FL317 the first officer stopped the descent by pushing ALT HLD and was instructed to climb to FL320, the aircraft climbed to FL320. The first officer then woke up the captain, who spotted FL292 on the FMS. The aircraft continued to Brussels for a safe landing without further incident.

India's Directortate General of Civil Aviation (DGCA) released their final report concluding the probable cause of the incident was:

The first officer inadvertently fed the Altitude window on Mode Control Panel with the corrected track of 292 Degree and activated thereby causing the altitude of the aircraft to drop.

The DGCA reported that the digital flight data recorder confirmed the aircraft was at FL340 with autopilot and autothrust engaged when the thrust levers were adjust back from about 58/59 degrees to about 50 degrees and the aircraft began to descend reaching a maximum vertical rate of descent of 1664 fpm. The aircraft climbed to FL320 about 3 minutes later.

The DGCA summarized testimony by the first officer: "The First Officer stated that the aircraft descended from FL340 without any pilot input until she arrested the descent AT FL317 using “ALT HOLD”. She became aware of the loss of altitude when she was queried by ATC. The Capt stated that he was taking controlled rest and was asleep at the time of the incident. He was woken up when the aircraft regained FL320."

The DGCA reported that the training records of the first officer showed no deficiency, all assessments after obtaining the type rating were satisfactory.

The DGCA analysed: "The aircraft was flying on westerly track which was between 230 and 300 degrees, the wind was approximately 240/45 kts. The Commander was under controlled rest during this period. While updating of heading 292 degree, in Turkish airspace the First Officer turned the altitude knob to 292 FL and pressed thereby causing the aircraft to descend. The Turkish ATC noticed the aircraft descent from FL340 to FL317. The ATC noticed the aircraft while descending below FL 320 and started calling about unauthorized descend. Subsequently, the First Officer pressed ALT HOLD and climbed back to FL320 Thereafter, the flight climbed to FL 320. The First Officer then woke up the Captain who was undergoing controlled rest. The commander saw 29200 feet on FMC when he woke up."

The DGCA summarized Analysis provided by Boeing:

Jet Airways provided the flight data, QAR data, and FMC BITE to M/s Boeing and asked to reproduce pilot input to MODE CONTROL PANEL at the relevant time based on the data.

M/s Boeing stated that - the FMC BITE analysis did not reveal anything that could be correlated with the reported un-commanded descent in cruise.

From the Boeing analysis report of the QAR and DFDR revealed that the following events took place:

“The airplane was flying level at FL340 (The MODE CONTROL PANEL altitude target window was also at FL340) with LNAV and VNAV mode engaged. At approximately 02:18:20 UTC, the MODE CONTROL PANEL Altitude was adjusted from FL340 to FL370, FL290 and then FL292 within 4 seconds. The QAR signal FMF_SEL_CRUISE_ALT signal shows a change from FL340 to FL292 approximately 10 seconds later, which indicates that the MODE CONTROL PANEL Altitude knob activated. The airplane responded per design, and began a cruise descent toward FL292. In addition, an EICAS ALTITUDE ALERT CAUTION was not present in the flight data. This annunciation would show if the aircraft descended more than 200 feet from FL340 (assuming that the MODE CONTROL PANEL Altitude remained at FL340). The data showed that the heading was 285 Magnetic (291 True) degrees at this time.

The airplane continued to descend from FL340 for approximately 1 minute and 45 seconds. When descending through FL318 the autopilot momentarily entered V/S (Vertical Speed) mode and then transitioned to the Autopilot ALT mode. This is consistent with the flight crew pressing the MODE CONTROL PANEL V/S button, then the ALT button. Approximately 2 seconds later, the MODE CONTROL PANEL altitude was adjusted from FL292 to FL320 but there was no MODE CONTROL PANEL Altitude knob press, so the FMF_SEL_CRUISE_ALT signal remained at FL292. The autopilot leveled at FL317. Approximately 35 seconds later, the MODE CONTROL PANEL altitude was changed from FL320 to FL340, but the MODE CONTROL PANEL Altitude knob was not activated. Approximately 10 seconds later, the VNAV mode was armed, and the AFCS immediately engaged in VNAV ALT mode at FL317, the target FMC altitude synched from FL340 to the current altitude of FL317, and the MODE CONTROL PANEL speed window closed.

Approximately 13 seconds later, the FMF_SEL_CRUISE_ALT signal rose from FL292 to FL340, consistent with the MODE CONTROL PANEL ALTITUDE knob being pressed. The airplane started to climb toward FL340. Upon climbing through FL320 the MODE CONTROL PANEL altitude knob was dialed down from FL340 to FL320 and the SEL button pressed, and the airplane then returned to level flight in the VNAV PTH mode. While the airplane was leveling it exceeded FL320 by 200ft and an altitude alert caution warned the pilots that the airplane had departed the MODE CONTROL PANEL altitude of FL320. The data showed that the flight continued normally thereafter.

This event does not appear to be similar to the condition reported in the FTD (Fleet Team Digest FTD Article 777-FTD-22-12001). In the past, MODE CONTROL PANEL window jumps have always been single jumps, and therefore only in one direction (increasing or decreasing, never jumping back and forth as in the subject event). Further, to date, there have been no window jumps followed by activation of the select knob.

Boeing is unable to identify an aircraft system failure that caused this descent. The available data does not the need to perform any additional aircraft maintenance in response to this event.”

The DGCA analysed that a simulator session was conducted to verify the events and stated: "The simulator findings and the DFDR analysis report submitted by Boeing are in concurrence with the observation made in the simulator exercise."

The DGCA concluded analysis: "During investigation it was also thought as to how this inadvertent flight level change or handling of control during the rest period could be addressed forthwith. The various flying pilots have stated that once the PIC is under controlled rest the first officer should desist from touching controls or effecting level change. Secondly, the cockpit being completely dark shall add to the fatigue at the end of flight. The PIC under controlled is akin to a situation as only one flight crew available in cockpit."
Incident Facts

Date of incident
Aug 8, 2014

Classification
Report

Airline
Jet Airways

Flight number
9W-228

Departure
Mumbai, India

Destination
Brussels, Belgium

Aircraft Registration
VT-JEL

Aircraft Type
Boeing 777-300

ICAO Type Designator
B773

This article is published under license from Avherald.com. © of text by Avherald.com.
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