Hydroplaning on Takeoff example

[jonny dangerous]

PK...I don't fly in to Newfoundland near as much as needed to stay proficient at this airport when the weather is not on your side.

I have thought about the first runway condition report we received that morning. I believe it was likely on the order of 50% bare and wet and a combination of ice patches or slush 1/8" for the remainder.

Under the circumstances, my F/O and I chose "Slippery" runway conditions to send via ACARS to get our T/O Performance numbers. After load figures were received by HQ, the server spit out the following (143,000 lbs TOW):

RW 11 8502 ft

TO-1 (Full 22K Derate), Bleeds On
Flaps 5
V1 106
VR 136
V2 141

Note the 30 Knot split between V1 and VR.

Resubmitting the same takeoff but using 1/4" slush or 1/4" standing water (they output the same) gave:

RW 11 8502 ft
TO (Full Rated 24K thrust), Bleeds On
Flaps 10
V1 120
VR 128
V2 134

Reconsidering the events of that morning and the changing state of the precipitation, I'm not sure I would have even left the stand. Knowing now, in hindsight, that a 727 would report "NIL" braking, it's a no-brainer.

I had to choose between slippery or 1/4" slush; I'm not sure either was appropriate. Given the differences in V1 between the two choices (as well as flap and thrust), it would seem appropriate to get the choice right. Perhaps on that day, lacking an up-to-date, reliable indication of runway contamination, it would have been prudent to delay pushback until a few landing big aeroplanes could have passed on braking reports. As there was slush and/or standing water on the runway, the aerodrome operator could not supply CRFI (Runway Friction Co-efficients) numbers.

As stated in an above post, the wind eventually favoured runway 34. There was the issue of the moderate to heavy rain and the standing water and the 40-60 degree crosswind at 35G45 kts to consider.

For 1/4" standing water/slush, submitting the same take off weight,and again at 0 deg C., gave the following for runway 34:

RW 34 7005 feet
TO (Full Rated 24K thrust)
Bleeds OFF
Flaps 25
V1 110
VR 124
V2 131

Note bleeds off and flaps 25. Once again, working pretty hard at sharpening the pencils.