Re # 20
PBL “
the flight crew's decisions were appropriate in light of the information they were given”
As an example see
http://www.skybrary.aero/bookshelf/books/1248.pdf
Selected extracts –
The landing was planned based on a dry runway with good braking action.
Based on the received information the crew did not expect any problems related to the weather or runway conditions.
The aircraft landed with 140 KIAS from a Vapp (VLS) of 147 KIAS. The speed was based on the correct Vref for the actual landing mass and increased 5 kt for Auto Thrust and 5 kt for icing conditions. This is in line with the company's standard landing procedures but is not optimal on contaminated and slippery runways.
The aircraft landed long with a soft touchdown … approx 3 kt tailwind … contaminated runway.
In hindsight – to be used for learning and not for blame, there could have been some mitigating activity.
“
The landing was planned based on a dry runway with good braking action.” Typically, factored landing data provides a margin for the normal day-to-day variability in height, speed, touchdown point, etc (but not all at once), and a choice of braking level. i.e. there is a safety margin which provides the basis of a mindset involving a normal operation – even complacency.
“
Three minutes before touchdown the crew were told that the runway was contaminated with 8 mm of wet snow and a braking action of 32-33-31 (MEDIUM). The crew made an assessment and decided that they were able to land with MEDIUM Braking Action… , it did not give the crew cause for concern with regard friction.”
If this assessment was based on contaminated landing data which was based on
CS AMC 25.1591 (approx page 710 in Am 9) then there may not have been any effective safety margin, even with the factors required by EU OPS-1.520 (b).
The published contaminated data may assume a threshold speed = Vref, touchdown 93% of Vref, 7 sec flare time, use of reverse thrust, etc, etc, and maximum braking.
Therefore it would be necessary for the crew to ‘reprogram’ the mindset from a normal – ‘data checked = OK’, to a contaminated landing special procedures mindset (speed / touchdown accuracy, max brake, full reverse) or even consider diverting.
We have opportunity to learn from the unfortunate culmination of factors experienced by others; we should not overlook such opportunities.