Emirates B773 at Melbourne on Jul 18th 2014, descended below minimum safe height on approach

Last Update: October 7, 2015 / 18:43:14 GMT/Zulu time

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Photo of Emirates Airlines A6-ECO, Boeing 777-300 — Emirates Airlines A6-ECO, Boeing 777-300 (Photo credit: tagsplanepics-lhr / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Jul 18, 2014

Classification
Incident

Airline
Emirates Airlines

Flight number
EK-404

Departure
Singapore, Singapore

Destination
Melbourne, Australia

Aircraft Registration
A6-ECO

Aircraft Type
Boeing 777-300

ICAO Type Designator
B773

Airport
Melbourne International Airport, Melbourne

Airport ICAO Code
YMML

An Emirates Airlines Boeing 777-300, registration A6-ECO performing flight EK-404 (dep Jul 17th) from Singapore (Singapore) to Melbourne,VI (Australia), completed the flight with a safe landing on Melbourne's runway 16 following an ARBEY standard instrument arrival.

Australia's ATSB reported however that the aircraft descended below minimum safe height during the approach to runway 16, an investigation into the occurrence rated an incident has been opened.

Radar data indicate that 12nm before touch down the aircraft was at about 2800 feet MSL (according to transponder altitude data corrected for QNH).

On Oct 7th 2015 the Australian TSB released their final report without conclusions but a safety message:

For operators, this incident highlights the need for careful attention to FMC navigation data management, particularly any procedures that relate to crew modification of navigation data. Operators should remain mindful that any manipulation of FMC navigation data by flight crew has the potential to introduce errors. Additionally, operators are encouraged to work closely with aeronautical information service providers to ensure that aeronautical charts (and any other operational information) are presented in a manner that minimises ambiguity and reduces the potential for misinterpretation.

For flight crew, this incident highlights the need for careful attention to approach procedure documentation and FMC navigation data management.

For producers and providers of aeronautical information products, a guiding principle specified in Procedures for Air Navigation Services, Aircraft Operations is to keep all charts as simple as possible. This may assist in reducing flight crew workload and the risk of error, and coding issues when entering data into flight management systems.

The ATSB reported that the standard arrival route guided the aircraft from waypoint ARBEY to waypoint BOL (an NDB) via waypoint BUNKY. A minimum enroute altitude of 3400 feet (and minimum terrain clearance altitude of 3700 feet) was defined on the STAR chart, however, no altitude constraint was shown at waypoint BOL, the initial approach fix for the RNAV procedure to land on runway 16. The RNAV approach chart showed an altitude constraint at or above 4000 feet while joining from an ARBEY approach and 3000 feet while joining from any other approach.

The ATSB reported that while overflying BUNKY the aircraft was cleared to descend to 4000 feet, about 5nm ahead of BOL the aircraft descended through 4000 feet with the FMC showing an altitude constraint for BOL to cross the waypoint at or above 3000 feet. The crew selected this to be an at 3000 feet altitude constraint. About 4nm before BOL the aircraft descended through 3400 feet, a minimum safe altitude warning activated at the controller's desk, the controller queried their altitude and advised that 3200 feet was the lowest safe radar vectoring altitude available. Moments later the aircraft crossed BOL at 3000 feet and maintained that altitude until intercepting the vertical profile of the RNP approach to runway 16.

The ATSB wrote: "A subsequent review of the ATC radar data showed that the aircraft left controlled airspace as it descended through 3,500 ft. The aircraft was briefly outside controlled airspace until it reached the 15 NM airspace boundary step, where the lower limit of controlled airspace became 2,500 ft. There was no report of conflict with other traffic outside of controlled airspace."

The ATSB analysed: "The operator’s investigation found that descent below the 4,000 ft altitude restriction at BOL occurred because the crew selected the ‘hard altitude’ of 3,000 ft for BOL. The potential for deviation below the 4,000 ft minimum altitude restriction at BOL was increased by factors related to aeronautical charts and the FMC navigation database. Some of these factors are discussed in the following paragraphs."

Airservices Australia, designing the approach charts, reasoned: "In controlled airspace, the approach procedures are designed to keep aircraft 500 ft above the control area steps. The 4,000 ft minimum altitude was designed to keep aircraft in controlled airspace prior to BOL, rather than for terrain clearance. Airservices further commented that a minimum altitude of 4,000 ft was not depicted on the STAR chart at BOL, as BOL was also applicable to the runway 27 arrival. This allows ATC to assign a higher altitude at that point for a runway 27 arrival due to potential runway 34 departures. No altitudes are depicted because two (or more) levels would be required to cater for the different runways. Only one level is permitted to be depicted against a waypoint (for a STAR) to avoid potential confusion as per Section 1-1-22 of Airservices 'Departure, Arrival and Air Route Management Design Rules' manual (ATS-MAN-0010)."

With respect to the FMC database the ATSB analysed: "Consistent with the STAR chart, the ARBEY 4U STAR FMC navigation data did not include an altitude restriction at BOL (Figure 6). FMC navigation data for the RNAV-U (RNP) runway 16 approach included an altitude restriction at BOL, but that altitude restriction was ‘3000A’ (meaning ‘at or above’ 3,000 ft) (Figure 7). The 3,000 ft restriction was applicable to a number of STARs that linked with the RNAV-U (RNP) runway 16 approach. But it was not applicable to the ARBEY STAR which had a 4,000 ft restriction."

The ATSB summarised Emirates' response: "The aircraft operator commented that they did not raise this issue with the FMC database provider, as the database coding reflects the AIP procedure design. The aircraft operator considered the conditional altitude over the waypoint BOL to be a procedure design weakness and raised that with Airservices Australia accordingly. The approach is no longer valid, but the operator intends to closely monitor for this issue in any new approaches."

Metars:
YMML 172300Z 22011KT 9999 FEW030CB 06/04 Q1021 INTER 2300/0200 6000 SHRA SCT020 FM2300 MOD TURB BLW 5000FT
YMML 172230Z 24010KT 9999 VCSH FEW030CB SCT033 06/04 Q1021 INTER 2230/0130 6000 SHRA SCT020 FM2230 MOD TURB BLW 5000FT
YMML 172217Z 23015KT 9999 -SHRA FEW020 SCT033 FEW031CB 06/04 Q1020 INTER 2217/0117 6000 SHRA SCT020 FM2217 MOD TURB BLW 5000FT
YMML 172200Z 22009KT 9999 VCSH FEW020 SCT033 FEW032CB 06/03 Q1021 INTER 2200/2300 5000 SHRA BKN012 FM2200 MOD TURB BLW 5000FT
YMML 172130Z 23013KT 9999 SHRA FEW022 BKN033 06/04 Q1020 INTER 2130/2300 5000 SHRA BKN012 FM2130 MOD TURB BLW 5000FT
YMML 172100Z 22015G25KT 9999 -SHRA FEW027 BKN037 07/04 Q1019 INTER 2100/2300 5000 SHRA BKN012 FM2100 MOD TURB BLW 5000FT
YMML 172030Z 22017KT 9999 FEW035 BKN055 07/04 Q1019 INTER 2030/2300 5000 SHRA BKN012 FM2030 MOD TURB BLW 5000FT
YMML 172000Z 24014KT 9999 FEW035 BKN057 07/04 Q1018 INTER 2000/2300 5000 SHRA BKN012 FM2000 MOD TURB BLW 5000FT
YMML 171930Z 24016KT 9999 FEW035 07/04 Q1018 INTER 1930/2230 5000 SHRA BKN012 FM1930 MOD TURB BLW 5000FT
YMML 171900Z 25015KT 9999 FEW035 07/04 Q1017 INTER 1900/2200 5000 SHRA BKN012 FM1900 MOD TURB BLW 5000FT
YMML 171830Z 24013KT 9999 FEW035 06/04 Q1017 INTER 1830/2130 5000 SHRA BKN015 FM1830 MOD TURB BLW 5000FT
YMML 171800Z 25016KT 9999 FEW025 BKN050 06/04 Q1016 INTER 1800/2100 5000 SHRA BKN015 FM1800 MOD TURB BLW 5000FT
YMML 171730Z 23013KT 9999 -SHRA FEW025 SCT030 BKN050 06/04 Q1016 INTER 1730/2030 5000 SHRA BKN015 FM1730 MOD TURB BLW 5000FT
YMML 171700Z 25018KT 9999 FEW030 SCT053 06/04 Q1015 INTER 1700/2000 5000 SHRA BKN015 FM1700 MOD TURB BLW 5000FT