Singapore B772 at Canberra on Feb 22nd 2017, descended below minimum safe altitude

Last Update: July 28, 2017 / 14:57:40 GMT/Zulu time

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Photo of Singapore Airlines 9V-SRP, Boeing 777-200 — Singapore Airlines 9V-SRP, Boeing 777-200 (Photo credit: byeangel / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Feb 22, 2017

Classification
Incident

Airline
Singapore Airlines

Flight number
SQ-291

Departure
Singapore, Singapore

Destination
Canberra, Australia

Aircraft Registration
9V-SRP

Aircraft Type
Boeing 777-200

ICAO Type Designator
B772

Airport
Canberra International Airport, Canberra

Airport ICAO Code
YSCB

A Singapore Airlines Boeing 777-200, registration 9V-SRP performing flight SQ-291 (dep Feb 21st) from Singapore (Singapore) to Canberra,AC (Australia), was on approach to Canberra's runway 35 about 18nm southsouthwest of the aerodrome at about 09:09L (22:09Z Feb 21st) when the aircraft descended below minimum safe altitude (7500 feet MSL). The aircraft climbed back to 7500 feet and continued the approach for a safe landing on runway 35 about 8 minutes later.

Australia's TSB rated the occurrence an incident and opened an investigation.

On Jul 27th 2017 the Australian TSB released their final report concluding the probable causes of the incident were:

- The captain manually entered the waypoint SCBSG into the FMC instead of selecting the RNAV-Z approach via waypoint SCBSG. This removed the 7,500 ft altitude constraint.

- The crew did not identify the aircraft had descended below the 7,500 ft minimum sector altitude prior to passing SCBSG.

- Prior to passing SCBSI, the flight crew elected to conduct a visual approach without advising air traffic control, the flight crew then descended the aircraft below the 5,300 ft segment minimum safe altitude.

- The aircraft was in visual conditions at all times.

The ATSB analysed that the crew was advised to expect runway 35. The ILS for runway 35 was not serviceable, the crew therefore prepared for the RNAV-Z approach and anticipated the standard arrival route (STAR) POLLI 4 PAPA. ATC subsequently cleared the aircraft for the VOR approach and assigned POLLI 4 BRAVO STAR, which the crew had not briefed for. Due to the similiarities between the approaches the crew decided to request the RNAV-Z approach later. A route discontinuity appeared in the flight management system after POLLI 4 BRAVO was selected into the FMS, which the captain resolved by connecting MENZI waypoint with waypoitn SCBSI, which however removed waypoint SBGSG and its altitude constraint at 7500 feet. The captain subsequently reentered waypoint SBGSG into the FMS, however, did not detect the altitude constraint. As result the aircraft descended below 7500 feet safe altitude, ATC radioed the crew when the crew was descending through 7000 feet and the aircraft climbed back to 7500 feet. The crew was visual with the runway and decided to perform a visual approach, however did not inform ATC which resulted in a second descent below safe altitude.

The ATSB analysed:

The flight crew planned to conduct the POLLI FOUR PAPA arrival and RNAV-Z approach. When ATC issued instructions for the POLLI FOUR BRAVO arrival and VOR approach, the flight crew accepted the POLLI FOUR BRAVO arrival while preparing to conduct the RNAV-Z approach, instead of the associated VOR approach. This lead to a discontinuity in the programmed flight path between the arrival and approach. The flight crew did not select the entry to the approach in the FMC and manually entering the waypoint SCBSG. As the waypoint was manually entered, the 7,500 ft altitude constraint was not included into the FMC programmed flight path. This missing altitude constraint was not detected by the flight crew.

The flight crew entered the altitude of 3,900 ft into the autopilot altitude selector prior to commencing the approach. With the autopilot engaged, the aircraft descended through 7,500 ft prior to commencing the approach at SCBSG. The flight crew did not detect that the aircraft had descended through the 7,500 ft MSA. The approach controller identified the error and alerted the flight crew.

Once established visual with the runway, the flight crew elected to conduct a manually flown visual approach without advising ATC, and did not receive a clearance to discontinue the RNAV-Z and conduct a visual approach. The aircraft then descended below the standard profile which led to the aircraft descending below the 5,300 ft SMSA prior to passing SCBSI.

Metars:
YSCB 230000Z 32010KT 9999 FEW055 29/12 Q1020 NOSIG
YSCB 222330Z 27005KT 210V310 9999 FEW050 26/12 Q1020 NOSIG
YSCB 222300Z 19003KT 9999 FEW045 25/12 Q1021 NOSIG
YSCB 222230Z 32003KT CAVOK 23/14 Q1020 NOSIG
YSCB 222200Z 33003KT CAVOK 21/13 Q1020 NOSIG
YSCB 222130Z 00000KT CAVOK 18/13 Q1020 NOSIG
YSCB 222100Z 00000KT CAVOK 15/13 Q1020 NOSIG
YSCB 222030Z 09002KT CAVOK 14/12 Q1020 NOSIG
YSCB 222000Z 00000KT CAVOK 12/12 Q1019 NOSIG
YSCB 221930Z 00000KT CAVOK 12/11 Q1019 NOSIG
YSCB 221900Z 15002KT CAVOK 12/11 Q1019 NOSIG
YSCB 221830Z 15003KT CAVOK 13/12 Q1018 NOSIG
YSCB 221800Z 00000KT CAVOK 14/13 Q1018 NOSIG