Incorrect ACAS recation leads to near miss

[J.O.]

Source: Flight International

Near-misses occur as pilots make ACAS reaction errors

DAVID LEARMOUNT / LONDON

Eurocontrol forced to reissue guidance on correct responses to anti-collision alerts

Eurocontrol has reissued advice to pilots on how to react to airborne collision avoidance system (ACAS) resolution advisories (RA) following a series of recent events in which crews have failed to follow procedures correctly and avoided disaster only through luck.

A frequent erroneous pilot response to an ACAS alert is incorrect reaction to the “adjust vertical speed” RA, triggered when aircraft are converging vertically at a high rate, says Eurocontrol. It cites an example of a near-collision that occurred because the pilot of an Airbus A319, climbing to flight level 260 (26,000ft/7,925m), reacted to an “adjust vertical speed” RA by increasing his rate of climb dramatically and maintaining it through his cleared flight level until the two aircraft passed each other with no vertical separation, but with 2.4km (1.3nm) lateral separation (see graphic).

The other aircraft, a Fokker 100, had been cleared to descend to FL270, but the pilot reacted correctly to a “climb” RA. Eurocontrol says that the correct reaction to an “adjust vertical speed” RA is always to reduce climb or descent rate – never to increase it – and although the frequency of this error is being reduced by improved ACAS training, conflicts are still occurring.

In an event evoking the 1 July 2002 fatal collision over Uberlingen, southern Germany, Eurocontrol describes how the pilot of a Boeing 767 converging with an A319 disregarded his ACAS “descend” RA and instead followed an air traffic control (ATC) instruction to climb, while the A319 pilot followed his “climb” RA. The aircraft missed each other vertically by 400ft (120m) and horizontally by 0.5km, says Eurocontrol. The conflict had arisen because the two aircraft, originally on converging headings but separated by 2,000ft vertically (the 767 at FL290 and A319 at FL270), were under the control of different ATC units in charge of lower and upper airspace, with a boundary between the two sectors at 28,500ft.

The A319 pilot asked for clearance to climb, and because of “a co-ordination error” was cleared to do so. The A319 crew received a “crossing climb” RA as it approached the 767’s level, and the 767’s ACAS gave a “crossing descend” RA – but it activated just after the 767 pilots had received a “climb immediately” instruction from the controller. They followed the advice. Eurocontrol has reiterated 10 rules, including “pilots must follow all RAs promptly and accurately” and “controllers must not interfere with pilots’ reactions to RAs”.

[UpperDeck]

I know. It has been said before but....if it's a "near-miss" then it's a hit, right?

[Kip Powick]

a 'near- miss' is a close call.(they were near but missed each other)

A 'hit' is normally followed with a great deal of noise

[Don Hudson]

Thanks JO;

This is another of many operational events which a Flight Data Analysis Program can track very effectively and provide feedback to crews in general on how their responses are doing, or if a crew contact is made by the Association FDA Gatekeepers, to provide positive feedback on a good response or some feedback on how it might have been better.

Depending upon how they are designed and depending upon the vendor and software employed for data analysis, FDA Programs can capture all details of a TCAS TA and RA including text of the corrective measures commanded. I haven't seen the capability yet of providing altitude and azimuth information of the intruder but perhaps that can be done in some Programs as well.

The patterns of TCAS advisories can be done by geographic location and altitude to enable targeting FDA messages to crews, perhaps even on the flight plans, for particular terminals, altitudes, approaches, times-of-day etc etc...all in the interests of flight safety. LaGuardia, as we might expect, is one such terminal but there are others crews are aware of.

Where response to a TCAS advisory is modified because the traffic is "visual", an FDA Program can assist in providing feedback to the operations people, the training specialists and line pilots.

Cheers JO,

Don

[plankspanker]

Do any of you know why instead of "Adjust Vertical Speed" the advisory isn't "Reduce Vertical Speed". Seems to me like that would limit the possible responses to the one desired.

[Don Hudson]

"Adjust Vertical Speed" (this might be the equivalent of "Monitor Vertical Speed" in other systems), references the command on the TCAS display. It is the first command during an RA and means fly to the green area on the IVSI display staying out of the red. If the rate isn't enough, the "Increase Climb/Descent..." or "Decrease..." etc occurs. If you're going to go thru the intruder's altitude while climbing/descending the commands are "Descend Crossing Descend", etc.