Originally Posted by
Buttscratcher
Righteo, so, given all of this knowledge, I'm assuming that you blokes (Curtain & 73 ) would have not departed Perth, or Diverted to an applicable Alternate?
Fair call, but what's your cut-off criteria for RF then?
Perhaps you have some applicable weather procedure or criteria to derive your Contaminated RWY no-go from the METAR alone?
I'm not trying to be recalcitrant, but if you have a workable method of ascertaining Contamination levels and braking action at uncontrolled Airports, please share.
I look at the METAR last 10 minute rainfall and rainfall since 0900 to give me a ballpark idea of the rain system. if you use 4.0mm per hour as the upper limit of moderate, just divide that by 6 (6 ten minute period per hour) is 0.7mm, If I am going somewhere short and ungrooved/non-PFC, I plug in RCAM Runway Condition Code 2 in the OPT.
If it is grooved/PFC I uses 7.6mm per hour, this equates to 1.2mm in the last 10 minutes before I plug in code 2. I then assess LDA vs required. If I can't do it, I hold then divert. I have diverted from a very short runway in the Whitsunday's (despite the CAVOK forecast, subsequent METAR showed 15mm of rainfall had occurred during the hour that covered our arrival period, tower reported visibility was between 900 and 1900m vis). At non-tower ports, you use the AWIS last 10 minute figure that is literally updated instantaneously, and is more useful that the slightly stale METAR.
Runway excursions globally are the
#1 cause of accidents according to ICAO. We are extremely fortunate in Oz, good weather, good runways so we don't think about it much. It rarely comes into play, but when it does, it's nice to be able to have in your back pocket, a plan of how to think about it. How many over-runs does it take to wreck a career? Honestly, you would be lucky to have to divert once every five or 10 years, but that diversion may CYA.
Extremely easy to justify to a manager why you couldn't land, as documented in the arrival period METAR rainfall. I would be extremely surprised if every RPT ops manual didn't have a statement along the lines of "don't land in heavy rain" so you are bulletproof, and your pax & crew are safe.
To me, the
Virgin Christchurch reduced braking effectiveness report gives you an idea of a real world scenario where the crew had limited time to make a choice of runways with incomplete information late in the flight with runway changes and how it can spin out of control pretty quickly and you find the end of the runway coming up very quickly. They stopped
5m before the end of the runway. Kudos to the crew for reporting it, this is a classic case study.
Originally Posted by ATSB Reduced Braking Action report
The captain assisted the FO with manual braking. Both crew reported that they could feel
the rudder/brake pedals ‘pulsing’, which indicated the antiskid system was operating. The crew
elected to keep reverse thrust deployed to assist with braking.
The FO reported that he was focusing on the red runway end lights and noticed the aircraft drift
slightly right, which he then corrected to bring the aircraft back onto the centreline. The captain
reported that, when reverse thrust was stowed near the runway end, there was enough surface
water on the runway to create a wall of spray. The FO reported that the aircraft came ‘slowly
sliding’ to a stop about 5 m from the runway end lights. The aircraft was then taxied to the
terminal.
It's not the first time I've heard of the "wall of spray" from the reverse thrust after the aircraft is stopped very close to end of the runway, the one told to me was Perth RWY24. Quite a few very close calls over the years that don't get talked about or reported,
If you look at Europe or the US, they are dealing with this frequently and have a much better understanding of the issues. EASA has an extensive report
A STUDY OF RUNWAY EXCURSIONS FROM A EUROPEAN PERSPECTIVE.
Airbus are now offering an A320 FMS upgrade mods to enable a real time braking performance:
Braking Action Computation Function’ (BACF)” derived as an objective figure to report, rather than a Pilot assessment. That shows that for a lot of the world, this is actually a big deal.
It's the silent sleeper issue, just waiting to catch the unlucky and unwary.