Hydroplaning on Takeoff example
 

Showed up at the airport the other day for 0615 L departure. Had already been delayed 24 hours by high winds and heavy snow.

The back side of the low pressure system had been dumping a mixture of rain, freezing rain and freezing drizzle.

The last runway report before we pushed was 90% bare and wet, 10% ice patches. No recent landers.

After type I and IV applications, we were preparing to leave deicing bay when a landed 727 reported "nil" braking (8400 ft runway). I observed where the 727 stopped and would assume that the pucker factor had been high on the rollout. Back to gate we go.

Some seven hours later, the wind is now favouring a different runway (7000 ft), the precip is rain and heavy rain (temp just above 0 deg C) helping to melt existing snow, and now there is a large pool of runway at the intersection of the planned departure runway, about 2000 feet down the take off roll. Various depths are reported: "1/2 inch+ standing water" was the one that got my attention.

We delayed further, but an Emb 145 eventually taxies out, sprays, and then commences the takeoff roll. I watched the takeoff and there was quite a spray back of water during intial roll, then a huge spray when the 145 entered the standing water pool. They continued takeoff without incident.

After a few minutes, one of the pilots radios back that there was hydroplaning on takeoff, and gave the estimated wind report (The airfield indicator had frozen up hours before).

We elected to delay the flight another hour or so and then departed without incident on a different runway. This was day six of a planned four pairing, so we were all motivated to leave.

My question to fellow bigger airplane drivers, have you ever "hydroplaned" on takeoff? Given the crosswind and the standing water, and the NG's fans sitting a few inches above the runway surface I thought it imprudent for us to depart with runway conditions as such. Especially since I had never heard of or experienced hydroplaning on takeoff. Water ingestion into the fans was also in the back of my mind.

I'm not questioning the 145's decision. Different airplane, different load. (We were 143K lbs at takeoff, 10K lbs shy of max takeoff wt.)

Jonny

Well it doesn't sound to me like safe conditions, so I would say you made the best decision based on available information, information by the way that would be used against you in case anything would happen to go wrong. As far as hydroplaning goes, it will happen anytime there is standing water, apparently the runway must be flat and not grooved, good call. :ok:

It was amusing running various takeoff condition calculations via our ACARS during the delay. As runway conditions, wind, and precipitation were changing constantly, it was probably a mug's game trying to put a number on contamination for instance. Slush was initially the cause of the ongoing battle to keep the runway clear. Then came the falling and melting water combo.

I kept a number of the printouts, some allowing takeoff and some not. Did a lot of leafing through CRFI and max crosswind recommendation charts.

At some points we were unable takeoff due to balanced field requirements, and at other times it was due to strong crosswind limitations.

One of those days where all you could do was to wait for the actual weather to reflect what was forecast.

Square root of the tyre pressure x 9

Here's the link to the airport diagram for our departure:

http://gc.kls2.com/diagrams/pdf/CYYT.pdf

Departure was initially planned off of runway 11.

After landing report of braking action "nil" on Rwy 11, departure abandoned.

Wind then increased to 35G45 Kts at 050 to 070 deg M.

Wind eventually started favouring Rwy 34 (020 Mag), according to the turboprop aircraft landing and departing throughout the period when the EMB 170's, A320's, and 737NG's weren't going anywhere.

Due to a lack of confidence in reports of runway 34 varying surface conditions, departure was further delayed. Large pool of water at intersection of Rwy 34 and Rwy 02. Melting snow and slush on runway 02 (which was never opened), coupled with strong gusty winds from north/northeast propbably pushed a lot of water onto intersection with 34.

Departure eventually accomplished on Rwy 11, when surface was 100 percent bare and wet, and wind was 10 Kts. The the visibility started dropping due to fog formation. With wind dropping, and temperature slightly above zero, the accumulated wet snow banks supplied a lot of moisture into the air.

At time of departure RVR was 1100 ft. Rwy 11 has centerline lighting so it was within our operating limits.

All above just for background.

I was planning to post the various thrust settings and V speeds for the two runways at varying contaminations. If no one objects. (Well, not many)


JD

Ken Wells

Remind me please --- Square root of the tyre pressure ( in psi) multiplied by 9. Answer in Kts or MPH?

So aquaplaning will always be hazardous on take off or landing when there is unbroken surface water. Also do you know where the spray is mostly directed from your nose wheel/s?

New types, for certification, often have to run nose wheel/s through sheets of water. Results may require use of chined tyres if there is risk of having the fires go out.

Not game to try a touch down and go round with a heavy on a smooth lake.

Handy to know the answer to the formula as applied to your car or the one you are pax.

Milt - my ref says knots.

900 Bpoc?
 

The departure procedure makes reference to 900 BPOC . Could someone help with a definition?

Thanks

Should this formula be applied to cars considering the considerable difference in tyre tread patterns between aircraft and car tyres.

Hydroplaning on takeoff?
Oh yes, been there and done that with a B707 at the old Taipei airport, runway 09.
Not an especially pleasant experience...:uhoh:

No, I don't think it should be. A bit of experience in standing water with many auto tires convinces me that tread depth dominates, and that aquaplaning is not present with good tires at speeds much greater than predicted by the formula mentioned here which I recall the reference saying was determined experimentally. For an extreme example, a light racing car with tire pressures around 1 bar can obviously lap a wet track a whole lot faster than 35kts with wet tires fitted.

And on the other hand, with high quality tires almost worn to the legal limit (2/32nds inch tread depth) I've experienced aquaplaning at very, very low speeds on smooth surfaces. I've been convinced for a long time tires worn anywhere near the legal limit have no business on the roads.

The departure procedure makes reference to 900 BPOC . Could someone help with a definition?


900 ft Before Proceeding On Course.

:)

Found a website of acronyms, Before Proceeding On Course was listed, but I haven't seen it before. :confused:

Formula is not for auto tyres. due to water displacment design technolgy.

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.

900 Bpoc
 

Thanks Torque2, not one I have seen before:ok:

I hope this link works. It's the weather report archives for the 19th March, 2008 at CYYT, the date and aerodrome of the above situation. All times in the chart are local times. Add 2 + 30 for UTC.

Our departure was scheduled for 6:15 a.m. Local.

http://www.climate.weatheroffice.ec....Month=3&Day=19

We didn't depart until around 3:00 p.m. local.

I'm in the process of trying to track down the forecast I had available, which called for the switch to rain much earlier than what actually happened.

Igh, I'm going through a number of the references you supplied. A genuine thank you.

Here's what went on the day before at CYYT St John's(March 18):

http://www.climate.weatheroffice.ec....Month=3&Day=18

Just to show what a lovely place it can be in the winter:)