View Full Version : Flex/Reduced Thrust Takeoffs & Deicing

18th Jan 2004, 07:26
Question for the experts.

After de-icing, is it permissable to flex (reduce) thrust on a uncontaminated runway? Why or why not?

Thanks in advance.

18th Jan 2004, 10:18
Reference B707 and L1011 AFM, yes, to your question...is allowed to use flex thrust.

Other aircraft...others will comment, i'm sure.

18th Jan 2004, 11:10
[After de-/anti-icing] "Takeoff operations with reduced thrust based on the assumed temperature method are permitted." [as long as the runway is dry].

This is from one of the 767 manuals.

If there is concern for using reduced thrust due to de- or anti-ice fluid on the wings, then refer to Boeing Aero magazine number 8 (the year 2000, I believe). There is a discussion concerning "fluid elimination" that addresses this topic.


18th Jan 2004, 21:23
737 3/4/5 OK: I believe the 200 has a 5 degree reduction in calculated assumed applied.

19th Jan 2004, 03:28
Yes it's OK to 'use'Flex/reduced' thrust now!origininally the flex was disallowed by certain carriers,same as in reduced VIS' case.
The other concern was the Takeoff speed requirement with the use of type 4(heavy)anti-icing fluid.(disallowed on some turboProps as the VR wasn't high enough to shed the fluid)
But the Industry seemed to have adopted the Flex'with deicing as a 'norm':D

19th Jan 2004, 22:43
Although some operators may allow a flex take off after de-icing i.e. there are no general regulations prohibiting it, this does not mean that there are no hazards. Remember that it was only during the last few years that the problems with type 4 fluids were discovered, these resulted in new procedures and limitations for many turboprop / regional aircraft, and proof of any hazard for larger jets is still in abeyance.

The using de-icing / anti-icing fluids contaminate the aircraft surfaces; all that you are doing is replacing one contaminant (of unknown effect – snow, ice) with another (with assumed known effects - fluid). Thus great caution is required when operating in these conditions. There are many various states that an aircraft can be in when treated with fluid; the type of fluid (1-4), the fluid-water mixture, the fluid spec (vendor), the conditions in which the fluid has been kept (age, heat), and the method and amount of fluid applied.

You may think that flexing will help your management, but they will not thank you after a mishap during winter ops involving de-icing / anti-icing fluids. Safety first, look after #1, especially during winter.

20th Jan 2004, 05:22
Right now, I think there are no restrictions for derated TO after deicing. But down in 1989 McDonnell Douglas Flight Operations Test Support stated that:

" When OAT is at or below 6ºC and fluids have been applied, the use of derated thrust is recomended only when the assumed temperature and associated take off speeds are determined based on an Equivalent Weight which is 5% above actual takeoff weight.
When OAT is above 6ºC, standard derated thrust procedures can be used if desired"

Few months later they promulgated new and more restrictive recomendations.

I guess that, as far as deicing fluids have improved since then, nowadays they slide more easily off the surfaces.

21st Jan 2004, 00:24
On another note, I once saw a 757-200 take-off where, because of one anti-icing system listed as inoperative, no derate could be applied. Why is that ? (didn't get a chance to ask at the time). It was a short flight on a winter day, light aircraft, long runway, dry, no wind, good viz.

21st Jan 2004, 00:57
You have an incorrect assumption about new fluids sliding off surfaces more easily. The problem with the new ‘thickened’ fluids (some type 2 and possibly all type 4) is that they may not flow off surfaces as quickly as the older fluids. This was in part the problems with type 4. Turboprop / regional aircraft have lower takeoff speeds than the big jets. These operating characteristics may not match the assumptions in the fluid specification.

If you still operate BAE SYSTEMS aircraft, see their latest All Operator Messages and the excellent booklet called ‘Think Ice 2000’. Also available in Spanish ‘Piense Hielo 2000’. I think that there is also a new CD on Winter Ops.

The UK CAA planned a Winter Ops CD with emphasis on de/anti icing procedures – ‘Ice Aware’; anyone seen this or have details?

21st Jan 2004, 02:56
There is an MEL item for the engine anti-ice valve locked in the open position that requires the use of normal (full) takeoff thrust. Associated with this MEL is also a RATOW and climb limit weight penalty of 22,400 lbs. That's a significant penalty for the 757.

21st Jan 2004, 03:33
Reduced thrust after de-icing.... yes

On a contaminated Runway? Not such a good idea. And certainly against policy at my company.

Kakpipe Cosmonaut
29th Jan 2004, 05:44
It also varies with countries. Here in tropical Canada, full power after anti-icing. ( i.e. Type IV )

29th Jan 2004, 06:24
Our US Carrier requires max power after deice regardless of runway conditions or clutter.