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High Power "Run Up" Before Take Off.

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High Power "Run Up" Before Take Off.

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Old 1st Jan 2019, 07:40
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High Power "Run Up" Before Take Off.

Morning all,
On numerous occasions I have seen various aircraft carry out Engine "Run Ups" to high power settings whilst holding the aircraft with the brakes. My question is would it be possible for the power available to push the aircraft forward even against "locked" wheels, ie scrubbing the tyres over the runway surface. Thanks.
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Old 1st Jan 2019, 07:58
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depends on the surface friction and the amount of power used.

If the engines are cold and we are going into icing conditions we need the oil temperature above a set value to have the ice protection working properly.

In general the power used is nowhere near 50% never mind 100% and both pilots are watching and any hint of movement and the power will be reduced. We would wouldn't call it high power settings it won't be more than the power used on approach to landing.

Each aircraft type is different though with what it uses. And there is a difference between the procedures for turboprops and jets.

There are also tables in the performance manual giving max power for warm up and braking action. So at say a good braking action of 0.40 you can use 30% and for a poor braking action of 0.15 (which is slip when you try and walk on it) then it will say only use ground idle and you just have to wait.
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Old 1st Jan 2019, 09:33
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IME when engines are run up after maintenance, aircraft are invariably chocked as well as having the brakes applied.

Though that might be something to do with having a hangar straight ahead of you instead of 6,000 feet of runway.
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Old 1st Jan 2019, 10:40
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Warbirds usually have a `collar` over the tailboom,linked to the u/c and then a dedicated ground picketing point set in concrete for high/full power runs,as well as chocks and brakes....
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Old 1st Jan 2019, 11:43
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At Farnborough, all departing Hunters were required to do a short full power burst when lined up then check engine instruments before opening up to roll; this was a result of an incident where a Hunter (XE531) experienced turbine failure just after takeoff which virtually severed the tail section behind the wing root, both pilots successfully ejecting at about 100ft.
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Old 1st Jan 2019, 15:01
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Many jets need a short run up on the runway just before take off. Usually something like 30 seconds at 70% N1 to shed any accumulated ice on the fan blades. Additionally to that there might be a requirement to do a run up like that for every 30 minutes ground operation in icing conditions. The brakes can hold that usually, unless braking action is too poor to take off anyway.
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Old 1st Jan 2019, 15:22
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Somebody who cannot be named bent a brand new 340 doing engine run ups. Didn't end well.
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Old 1st Jan 2019, 15:35
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https://www.flightglobal.com/news/ar...340-60-319969/



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Old 1st Jan 2019, 18:44
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Well Hoskins, at least you got the gear down.
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Old 2nd Jan 2019, 10:20
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Originally Posted by 763 jock View Post
Somebody who cannot be named bent a brand new 340 doing engine run ups. Didn't end well.
Except that nobody from the unnameable airline was on board!
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Old 2nd Jan 2019, 14:10
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Originally Posted by chevvron View Post
At Farnborough, all departing Hunters were required to do a short full power burst when lined up then check engine instruments before opening up to roll; this was a result of an incident where a Hunter (XE531) experienced turbine failure just after takeoff which virtually severed the tail section behind the wing root, both pilots successfully ejecting at about 100ft.
That was a 200 series avon as per F6/9 which as part of i think air test was to confirm brakes wouldn't hold at end of runway whereas the the 100 series in T7/GA11 etc would hold if i remember correctly , this was standard before the 531 crash
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Old 2nd Jan 2019, 14:44
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Originally Posted by Groundloop View Post
Except that nobody from the unnameable airline was on board!
It was an ADAT employee in the left hand seat.
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Old 3rd Jan 2019, 07:31
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Many thanks for the replies, so then the general opinion would seem to indicate that the answer to my question is "yes". Thanks again.
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Old 3rd Jan 2019, 10:53
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During my days as a "Phantom Fitter" we used to position Phantoms up a ramp to prevent the jet efflux unrolling the tarmac/concrete during max power runs. Chocks would be positioned, brakes on, restraint chains attached to the main landing gear and the the lowered arrester hook and all attached to concreted in ground anchors.
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Old 3rd Jan 2019, 13:06
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Seem to remember the Phantom could actually rotate the tyres on the wheels at max chat on brakes.
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Old 3rd Jan 2019, 13:16
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Many thanks for the replies, so then the general opinion would seem to indicate that the answer to my question is "yes". Thanks again.
It is yes but day to day with pax in the back I would say it would be extremely unusual for pilots to use a high power setting with the brakes set.

Technicans doing power runs different story.
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Old 3rd Jan 2019, 13:24
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Some airlines have a winter ops proceedure to increase power setting once lined up for take off for 30 seconds or so after carrying out de-icing. Two of my previous uk employers did this anyway.
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Old 4th Jan 2019, 00:08
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A320ís needs an engine run-up every 30mins in ground icing conditions. Increasing to every 10min when freezing rain/drizzle/fog or heavy snow.

Run up needs to be 70% N1 as a minimum, repeated again before the take off roll commences. So a very common thing to do, 99% of the time just done on the runway before releasing brakes for take off.
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Old 4th Jan 2019, 04:08
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The Russian Air Force seem to have a policy of 'full chat' for at least a minute before letting the brakes off.
I saw a BACKFIRE bomber doing it recently, and it was mighty impressive as the aircraft generated a giant plume of filthy yellow smoke behind it.
To be fair, he only lit the burners on rolling....

IL-76 pilots also habitually do this, I think it's some sort of proof test, in case the donkeys chuck it once they get airborne.
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