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Old 24th May 2007, 10:41
  #19 (permalink)  
old,not bold
Join Date: Apr 2006
Location: uk
Posts: 758
Stopways........I wonder how many airports in UK, the rest of the EU, and world-wide have been asked by its regulator to produce evidence of tests? Perhaps airlines need to be more pro-active here. But I think the point's been made enough in this thread.

RESA's. As Overun says 90m is the minimum. But there's more to it of course. In the UK at least "licensees should not assume that 90m is sufficient" and they are required to review their RESAs once a year, taking into account a large number of factors including a change in the type of aircraft and traffic level, navaids, overrun history and so on. A 240m RESA is "recommended" for Cats 3 and 4, notwithstanding this review.

It seems to me, on consideration, that there is understandable confusion between the roles of the stopway and the RESA. The RESA serves several purposes, including when an aircraft "undershoots" (CAP 168's term, not mine).

But among those purposes, the RESA is there to "minimise risk to aircraft and their occupants when an aircraft overuns .. a runway". Hang about; the stopway is "an area of ground beyond the TORA which is...a suitable area in which an aeroplane can be stopped in the event of an abandoned take-off".

This appears to mean that a RESA is provided, in the over-run case at least, as a secondary stopway if the aircraft cannot be stopped within the ASDA. But why? the whole idea is that the aircraft an be stopped within the ASDA under all circumstances, and its take-off weight is adjusted, if neceesary, to achieve this.

Is this simply a pragmatic recognition that stopping distances achieved in manufacturers' tests are unrealistic in real life?

If we accept that, the problem then is that the RESA surface "should enhance the deceleration of aircraft in the event of an overrun"; it might even contain an arrester bed. Thus if the aircraft leaves the stopway heavy and still rolling with any speed, structural damage is predictable, with consequent higher risks to passengers and crew.

Surely there needs to be some clarity about this? If there is any risk whatsoever that an aircraft cannot be stopped safely and without risk of structural damage within the declared ASDA, that risk must be eliminated. It is a fudge to use the RESA instead of eliminating the risk of not stopping within the ASDA, because using the RESA as additional stopway simply creates more risks.

Surely the correct solution is to make sure that the declared ASDA is absolutely up to the required standard along its whole length (or if not to assess and use the real ASDA), and to review the way in which accelerate-stop performance is calculated so as to provide a 100% probability that an aircraft can be stopped within the ASDA under all circumstances (including an allowance for load sheet inaccuracy, among all the other adverse factors like weather, crew pissed off by security, etc etc).

I do realise that the response is likely to be, "Get real, it'll never happen. You'll have us reducing payloads next. And that's money." But there's no harm in being aware of the issues. And I still get nervous in the back on intersection take-offs, just to help the traffic flow or whatever.
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