finals24

My company has a policy not to permit assumed temperature take-off thrust reductions after an aircraft has been de-iced. When questioned, the powers that be respond that this is a Boeing recommendation and is due to residual fluid left on the wings causing a reduction in lift, therefore full thrust take-off's are mandated.

Looking at the Boeing FCOM for the 737NG this is not the case. Boeing specifically permit assumed temperature reductions after de-icing (interestingly this also used to be included as a paragraph in the FCTM but has been removed).

I would be interested to hear of other people's experience and views on this subject.

BOAC

Memories getting rusty here, but BA USED to have a 4 deg buffer for assumed after deicing on the Classic which was. I think. eventually dropped. I have asked my company the same question. If the para has now been 'removed' I guess each company would need to seek a 'no objection' from Boeing.

PEI_3721

IIRC the first Boeing view is more likely. Residual fluids are believed to reduce the aircraft climb performance, thus it would be poor practice to allow a reduced performance take off where a further reduction is possible.

Another thought is that where de-icing is used widely, then the fluid departs the wing during take off, with the majority being shed at rotation. The fluid remains on the runway just where max braking might be required in the event of an RTO. A full power take off would enable a larger safety margin.

flywestjetcr

The only limitations we show in our WestJet NG SOP's to using Assumed Temperature Method is when the runway is slippery or contaminated. In these cases it is prohibited. Full De-Rate is permitted and is preferred when the runway meets these conditions. We do not apply any penalty to having fluids on our wing. In my opinion, the wing is considered clean at rotation and therefore the amount of thrust applied to attain this speed is inconsequential.

Cheers

flywestjetcr

Have your guys call the Flight Technical guys here at WestJet if they want. We operate in the white stuff for many months of the year and our guys are really knowledgeable in this area. Last year we provided some winter ops training to the NZ Air Force who were training up on the NG. I think your company is wasting money on launching at full rate after a de-ice when it's not required.

Cheers

Denti

Yup, same here. Only restriction is degraded braking action or contaminated runway (which we often have when we have to de-ice). If braking action is good and no contamination we can use derate and assumed temperature same as usual even after de-icing.

BOAC

- a total 'Red herring' I think?

IF - and a big IF, there is a possible loss of wing efficiency due to remaining de-icing fluid, there should be a reduction in RTOM publshed for full power take-offs. Since there is none (737), either Boeing are legally liable for a deficiency or it is not relevant.

finals24

Many thanks for the replies to my original post. They do confirm what I suspected in that there is a variation in policy adopted by different operators. The Boeing 737NG FCOM contains the following paragraph:

Testing of undiluted de-icing/anti-icing fluids has shown that some of the fluid remains on the wing during takeoff rotation and initial climb. The residual fluid causes a temporary decrease in lift and increase in drag, however the effects are temporary. Takeoff operations with reduced thrust (assumed temperature method or fixed derate) are permitted provided takeoff performance accounts for the runway surface condition. Use the normal rotation rate.

Given the potential cost, in terms of engine wear, of not derating and Boeing's acquiescence with derating, I am very suprised that some operators continue to adopt a policy of not derating after de-icing.