Wrong reaction to “Adjust Vertical Speed” RA

[alf5071h]

Eurocontrol Safety Alert:- 2 June 2006 reminds pilots:-

1. It is necessary to observe carefully the RA display when manoeuvring, bearing in mind that an "Adjust Vertical Speed" RA always requires a reduction of the vertical speed.
2. All RAs are to be followed accurately, even if there is a discrepancy between RA and ATC clearance or instruction.

Reasons:-

1. There are repeated instances of pilots incorrectly executing “Adjust Vertical Speed” RAs.
2. In some cases, this wrong reaction to this actually led to the deterioration of spacing between the aircraft.

Info:-

1. TCAS II is designed to generate an “Adjust Vertical Speed” RA instead of a stronger “Climb” or “Descend” RA, whenever possible.
2. The objective is to solve a predicted risk of collision by a reduction of the current vertical speed, either in climb or in descent, while maximising compatibility with the ATC clearance. The reduction is associated with four different values: 0, 500, 1000 or 2000 fpm.
3. RAs could occur when aircraft are in close proximity and the vertical speed of closure exceeds 1500 ft/min;
4. This type of RA is mainly issued when an aircraft is climbing or descending to level-off 1000 ft from another aircraft. It reinforces the controller’s clearance and helps to ensure successful level-off at the cleared flight level.
5. “Adjust Vertical Speed” RAs are the most frequent RAs triggered by TCAS II.

See ACAS Bulletin No.3

N.B. “Adjust Vertical Speed” RAs always require a reduction of the vertical speed

Also see ACAS Safety Information.