Stabilize engines before rolling

[punkalouver]

I read somewhere that this is a requirement in Europe under JAR-OPS 1. Does that mean you never see rolling takeoffs in Europe? Is there a North American equivelant regulation? Do Foreign carriers have to follow this regulation while operating in Europe? Thanks.

[CaptainSandL]

I was not aware that it was a JAR-OPS requirement and I would doubt that it was. Anyway, rolling take-offs can still be done because you only have to have the engines stabilized at a low power setting before applying take-off thrust, which can be done whilst lining up.

[behind_the_second_midland]

You don't have to be stationary to "set power", stabilise and call "power set".

[Dehavillanddriver]

IT is a question of having takeoff thrust set at the commencement of the take off roll to ensure the the performance requirements can be achieved.

Boeing state that the increase in takeoff distance is "negligable"

However how do you quantify what is negligable?

I have seen many guys/gals roll many many metres whilst they stuff around like old women setting 40% N1 and then dithering a bit more for good measure then hitting the TOGA buttons.

Rolling starts, whilst the norm, have the "potential" to invalidate the takeoff performance figures. Before people tell me that I am alarmist, I think you will find that the takeoff performance figures are predicated on having takeoff thrust set within the line up allowance - which for most smaller jets is within the piano keys at the end of the runway.

John Tullamarine can expand upon my comments more eloquently than I can.

[The Stooge]

What about method A or C takeoffs where thrust/power must be set by 40 or 60 kts ?

[Dehavillanddriver]

It makes no difference, the thrust - in order to meet the performance chart criteria should be set within the line up allowance.

Boeing simply state that setting thrust on a rolling start has a negligable penalty.

The reality is that it rarely makes any difference, but to be totally accurate that is what is supposed to happen.

Statements like set thrust by 40 or 60 knots are difficult because there is no way of quantifying where 40 or 60 knots is in relation to the start of takeoff - which means that there is no way of ensuring that the performance figures that the ops engineer has worked so hard to calculate and that you have gone to all the trouble of extracting are near to meaningless - unless you are happy to exit the end of the runway at 40 or 60 knots in the event of a reject - or are prepared to compromise your 35 ft(+gross to nett margin) obstacle clearance in the event of a go..

Like I say it is mostly semantics because it rarely makes any noticable difference in real life operations.

[Flight Detent]

Hi all,
I've not heard of that requirement to set t/o power within the lineup allowance, that's only about 75 feet ASDA for a B737-700!

I understood that the 40% N1 was to be stabilized for only a max of 2 seconds before advancing the power, otherwise the t/o field length may be compromised.

Cheers, FD:uhoh:

[barit1]

Boeing state that the increase in takeoff distance is "negligable"

Mr. Boeing is right. Rolling vs static TO difference is way down in the "noise" of performance data.

Other examples of this data noise:

Gusty wind
Variations in runway slope
Assymetrical thrust set

It's a science, but not all the unknowns can really be quantified.

(And there's a decreased risk of FOD using rolling TO technique...)

[john_tullamarine]

Several things at work, here ..

(a) the aircraft is moving (ex lineup) which is a plus (some speed versus stationary)

(b) the presumption is that thrust is set without undue delay .. as in, typically, spin up, a quick check of the gauges, TOGA. Now, I haven't flown the NGs but I presume that they aren't too different from the classics where the whole lot can be done in the last bit of the alignment with the runway direction - ie, by the time the aircraft is pointing in the right direction, thrust is coming up to the takeoff setting. Folk should keep in mind that there is nothing wrong (on normal width runways) with starting the roll off centreline and coming back in the first few hundred metres.

(c) where there may be a concern is on a short runway (or intersection departure) at light weights where the aircraft can roll a reasonable distance at low thrust. In such cases it is important not to play about too much .. the aim is to get the aircraft rolling in the right direction with thrust set as soon as is reasonably practicable.

[Dehavillanddriver]

John, you are correct the NG is reasonably fast to spool up.

I was thinking more of the case where guys (gals) line up by following the taxi off lines, stop, get a clearance to takeoff, release the brakes, start rolling whilst they faff about setting 40% to the 8th decimal place and then eventually hit the toga buttons.

IF the crews line up in the line up distance and keep it rolling I agree that there is no drama, but the scenario described above happens quite regularly unfortunately and means that people are not really aware of what they are trying to achieve.

Sydney 16L is a good case in point where it has a displaced landing threshold, but the start of takeoff is at the runway entrance, people see the piano keys and almost taxi up to them before getting going - a recipe for disaster!

[john_tullamarine]

While generalisation has its problems .... the suggestion that folk do the following ..

"I was thinking more of the case where guys (gals) line up by following ..."

defeats the philosophy behind the use of rolling starts.

However, one needs to consider where the critical TODR/TORR/ASDR start for a particular aircraft/runway/ambient combination. If the roll starts several thousand feet before that point, the significance of the concern is less .. other than for the quite important question of standardisation in operational practices. So, for instance, SYD 16R, from past memory ... is a LONG runway for most small birds ...

.. and, as most of us probably can attest, having hit the TOGA switches ahead of plan during the initial takeoff roll ... the consequence is only one of coarse use of pedal steering to minimise any embarrassment .. directional control of the aeroplane is not a real concern.

The consideration of actual weight is important .. at high GW, one needs a fair bit of thrust to achieve breakaway so the problems with a tardy thrust setting is not so significant.

[mutt]

I think you will find that the takeoff performance figures are predicated on having takeoff thrust set within the line up allowance

Be very careful about this, it not only has to do with the model of aircraft, but also with the software used for calculating the takeoff weight.

We use two versions of Boeing supplied and approved software. The older version doesnt have the ability to account for line up distance, the new version does, but doesnt work on a mainframe computer.

Its best to check what your airline policy is regarding the amount of line up distance used in the calculations. BTW, we operate under FARs.

Mutt