BOI into the 2012 Tornado Collision over the Moray Firth

[Distant Voice]

What is ALARP?

In 1991 a specification was drawn up for Fast Jets for a piece of airborne equipment "to enable a very significant reduction in the risk of mid-air collisions"; in effect make the collision risk ALARP. The specification called for;

(1) Combined closing speed of 1000 kts
(2) Host bank angle of 60 degrees with 15 degree roll rate/sec
(3) 2g turns by host aircraft
(4) Maximum search range of 18 nm
(5) +/- 60 degree of azimuth from host's boresight and +20 degrees and -10 degrees of elevation
(6) Operates within the altitude range 200 - 5000 ft
(7) Provide alerts within 15 secs to interception (Tau). (a) Threat level 1, where Tau is between 5 and 15 secs. (b) Threat level 2, where Tau is between 0 and 5 secs, of pop-up target at 2 nm or less.
(8) Discriminate between threats separated by at least 1 nm in slant range.

The flight trial results and the 1998 OR(Air) document make it clear that the specification was met. Unfortunately, the programme was halted and with it the progress towards ALARP. Despite all the "smoke and mirrors" between 1998 and the time of the Moray Firth collision, the specification requirement was not fulfilled and the risk of collision remained NOT ALARP.

Currently, we are in the process of evaluating a piece of off the shelf equipment which falls short of the 1991 (ALARP) specification, and as a consequence the collision risk remains NOT ALARP. Probably that is the reason why the Risk Register shows no projected change in the Risk Index after TCAS has been fitted. It now seems a case of fitting any collision warning system simply to address the "societal concern".

N.B. This shold be read in conjunction with posting #250 "What is Tolerable"

DV