Singapore B773 and Delta A319 at Houston on Jul 3rd 2014, loss of separation

Last Update: November 27, 2015 / 17:15:20 GMT/Zulu time

Bookmark this article

Photo of Singapore Airlines 9V-SWH, Boeing 777-300 — Singapore Airlines 9V-SWH, Boeing 777-300 (Photo credit: Alec@B92 / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Jul 3, 2014

Classification
Incident

Airline
Singapore Airlines

Aircraft Registration
9V-SWH

Aircraft Type
Boeing 777-300

ICAO Type Designator
B773

Singapore Accident Investigation Board (SAIB) released their factual report reporting, that the United States NTSB did not formally investigate the occurrence due to being regarded as a pilot deviation from an ATC clearance after reviewing the occurrence with the FAA. The SAIB however considered the occurrence significant enough to warrant a formal investigation receiving input from FAA and NTSB. The investigation concluded without a formal conclusion to the cause of the loss of separation event.

The SAIB reported that Singapore Airlines' Boeing 777-200 departed Houton's runway 15L with the captain (C1) being pilot flying and the first officer being pilot monitoring, a second captain (C2) was occupying the observer's seat. The aircraft was cleared for the INDIE ONE RNAV departure. Neither crew member had flown that departure route before.

The crew used Jeppesen charts from their electronic flight bags. The captain read the first line of the route description then scrolled down to the pictorial portion of the chart checking tracks and distances and without returning to the text portion of the chart concluded that there were no altitude restrictions. However, the text describing the route read:

From RENNK on track 016° to COLET, then on track 025° to SUSHI, then on
track 026° to INDIE, then on transition. MAINTAIN 4000' or as assigned by
ATC. EXPECT filed altitude 10 minutes after departure.

The planned cruise level was 310. The captain expected to be issued some sort of intermediate altitude restriction however and planned to query ATC should ATC not provide an altitude restriction by himself, the captain did not communicate his plan to the first officer though, so that the first officer was not aware and could not remind the captain later.

Following departure and upon contacting departure control the aircraft was instructed to follow a heading of 020 after climbing through 2500 feet, the first officer however did not communicate their target altitude to ATC. When the aircraft climbed through 5600 feet the TCAS issued a "TRAFFIC TRAFFIC" aural alert, soon after ATC urged the crew to descend to 5000 feet in urgent tone. The captain disconnected the autopilot and initiated a descent, soon after TCAS issued a resolution advisory "Climb! Crossing Climb!" The captain did not comply with that resolution advisory and continued the descent, 19 seconds later the TCAS issued another resolution advisory "Level off!", another 8 seconds later TCAS announced "Clear of Conflict", the B777 was about to level off at 5000 feet.

Overall the resolution advisories were active for 27 seconds, 1000 feet vertical separation was restored within 10 seconds after separation had eroded to 200 feet vertical and 0.61nm horizontal.

Following the event the second captain queried whether there had been any altitude constraints in the departure route, all three pilots had missed that constraint mentioned in the route description text. The second captain reviewed his copy of the departure chart, discovered the altitude constraint and pointed the constraint out to the other crew members.

The SAIB stated: "The “climb via SID” clearance (see paragraph 1.1.9) is a new phraseology and procedures introduced by the Federal Aviation Administration (FAA), the US ATC authority, on 3 April 2014. ... A clearance for a SID which contains published altitude restrictions or ‘top altitude’ is issued using the phraseology “climb via”. The “climb via” is an abbreviated ATC clearance that requires compliance with the procedure lateral path, associated speed restrictions, and altitude restrictions along the cleared route or procedure. When the top altitude is included in the SID route description, controller will instruct aircraft to “climb via SID”. The top altitude is the charted “maintain” altitude contained in the procedure description or assigned by ATC. The filed flight plan altitude is not relevant, and has no bearing on the SID unless communications are lost between the pilot and ATC.", in other words:

a clearance "climb via" always and always contains an altitude restriction.

The SAIB discussed that the crew was not systematic in conducting their departure briefing. By aborting reading the text description and zooming into the pictorial part of the departure chart all crew members missed the altitude constraint at 4000 feet.

On the other hand, the SAIB discussed, had the altitude constraint been depicted more prominently in the pictorial part of the chart, too, the flight crew might have picked up on that contraint and reasoned: "As it was, the SID’s altitude restriction was not found in the ‘Initial Climb’ section, but was in SID’s text box under the ‘Routing’ section. It is not intuitive to look for information on altitude restriction for the Initial Climb phase in the ‘Routing’ section."

The SAIB continued the discussion: "During the initial radio contact with Houston Departure Control, the PM reported that the aircraft was climbing passing 2,500ft but did not report the altitude that the aircraft was climbing to. There was also no request made to determine the cleared altitude in the departure phase. The Flight Crew Training Manual (FCTM) on standard radio communications phraseology requires pilots to articulate both passing altitude and assigned altitude in their initial contact with a radar departure frequency, as well as following other frequency changes in a radar environment. ATC would likely have stopped the climb at 4,000ft or 5,000ft if the crew had communicated their intention to climb to FL310."

The SAIB concluded discussion: "The flight crew understood that all RA commands must be complied with even if they are in conflict with any ATC instruction. The PF stated that he had experienced TCAS RAs in actual flight before but not a “Climb, Crossing Climb” type. C2 and the PM stated that it was their first TCAS RA in actual flight. This could partially explain the delayed crew responses and incorrect execution of the RA climb command."

The operator took a number of immediate safety actions with respect to TCAS response and cockpit resource management as well as reminding crews in a circular letter that they should be aware of altitude restrictions on SID charts and check with ATC if any doubts.

The FAA changed the layout of the SID chart depicting the top altitude (4000 feet) prominently at the top of the pictorial part of the standard instrument departure chart.

The SAIB stated, that they were satisfied with the safety actions already taken so that no safety recommendations were needed as result of the investigation.