How Two Airliners Were on Collision Course Under Investigation

Tue, Dec 29, 2009 — David Evans

Articles, Featured

Much can and should be done to reduce the risk of a midair collision, but action is apparently lagging. The 22 December case of a Cathay Pacific A330 and a Virgin Blue B737 flying in opposite directions at 37,000 feet over Australia is a good case in point. Note that both aircraft were at the same flight level, the B737 northbound and the A330 southbound.

The Australian Transport Safety Bureau (ATSB) is investigating. So far, the ATSB characterizes the “serious” incident as a “breakdown of separation.” Few details have been released, but here is what the ATSB says:

“An Airbus Industrie A330 was southbound at FL370 and a Boeing Company 737 was northbound on the reciprocal track also at a non-standard FL370. When the crew of the A330 questioned the [air traffic] controller, the controller instructed the A330 crew to climb to FL380 and cleared the aircraft to divert right of track. The crew of the 737 then advised the controller they were diverting 10 NM right of track. There was a breakdown of separation standards. The investigation is continuing.”

A bureau spokesman said it was unlikely the planes had been close to colliding, given that neither of their TCAS (Traffic Alert Collision Avoidance System) had sounded a “resolution advisory.” He said a final report should be completed by April.

Given that the incident occurred late at night, it is fortuitous that the A330 crew was awake and alert.

To sum up the situation: aircraft are forced down narrow corridors, thereby greatly increasing the risk of a mid-air collision, while at the same time justifying the job of the air traffic controllers to keep them apart.

The incident has spawned some interesting pilot and air traffic controller commentary:

Pilot 1:

“It’s kind of funny to reflect that we fly designated air routes (railway tracks in the sky) at set altitudes within =/- 50 feet vertically and =/- 100 meters laterally to such an extent that two aircraft pass each other at 1,800 km/hr in the middle of absolutely nowhere on a regular basis with only 1,000 ft of separation. The much reduced probability of this happening if aircraft used random tracks and altitudes in remote areas (no ATC) would seem to be a better option.

“I’ve noticed that some carriers seem to spend a lot of time at non-standard levels, chasing that extra bit of gas by being 1,000 ft closer to optimum. Non-standard levels are a risk, especially outside radar coverage. At any non-standard level, one should fly a strategic lateral offset. The accuracy of modern navigation systems is too good, as the GOL collision over the Amazon proved. [See Air Safety Journal, ‘Complacency & Computer Perversity Lead to Brazilian Mid-Air Collision’ involving the impact at 37,000 feet over the Amazon between a GOL B737 and an EMB-135 business jet.]

“Flying on North Atlantic routes, pilots now have the approved option of flying 2 NM off track (to the right); this beautifully resolves the head-on case and the difference in speeds of following traffic should really make it a non-event.

“What irks even more are people who ask for block levels covering about 4,000 ft. In turbulence, maybe a 2,000 ft block can be justified, but some carriers are just plain inconsiderate when regularly requesting block levels. In the last amendment in the ATC section of Jeppesen [charts], it now states that any request for a non-standard level has to include the phrase ‘due to operational requirement.’ I would not consider winds or travelling closer to optimum level an operational requirement unless fuel critical. Maybe ATC needs to be less generous with non-standard level approvals unless pilots start using this phrase and they have a genuine need for a non-standard level. Something to consider.”

Air traffic controller 1:

“The problem associated with the non-standard level debate is that unfortunately these shortcuts are sometimes required to facilitate an expeditious flow of traffic. During the night over central Australia there can sometimes be up to 30+ aircraft in a conga line … Without non-standard levels we would have people cruising at FL280 etc.

“However, it must be said that whenever a controller assigns a clearance then separation becomes his/her responsibility. We can say we are all pissed off/fatigued etc but once we plug in and assume control we are bound by law/duty to perform our safety assurance role.”

Which elicited the following response:

“So, having, say, chosen to approve a non-standard level at, say, 3 in the morning (or any time, really) what are you personally going to do to mitigate against the possibility that you might not notice someone coming the other way? …

“Just how good is TCAS at resolving and averting an 1,800 km/hr head-on collision? …

“In a modern navigational environment, two way routes are a dangerous and stupid anachronism. It takes only a little imagination to establish race tracks where possible; and where there isn’t room for race tracks, formalize the strategic lateral offset.

“The large navigational tolerances ATC apply to aircraft are largely fantasy in this day and age. If two are going to hit in the cruise, it will happen on track, not 14 NM either side of it.”

Clearly, the ATSB has a great deal to address in investigating this “breakdown of separation standards.”

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