Determination of TO speeds and use of FLEX/TOGA at very low TOW

[flavioromero12]

Gentlemen,

After checking the FCOM Airbus 320, PER-TOF-TOC-12-30 EXTRAPOLATION

For a takeoff weight lower than those displayed on the chart, associated speeds are calculated as follows :
1. For given configuration and wind, note the speeds associated with the takeoff weight in the row displaying the highest permissible temperature.
2. Apply speed corrections provided at the bottom of the RTOW chart to V1 , VR and V2 limited to the minimum speeds.

Which means we need to subtract 1 Knot to V1/Vr/V2 per TON (1,000 kg) to that weight displayed on the last row of the RTOW chart (considering the wind conditions) limited to the minimum speeds displayed on the RTOW chart.

And then use those speeds for Takeoff.

Now, the questions is:
Considering EXTRAPOLATION (FCOM PER-TOF-TOC-12-30) is only mentioned on TAKEOFF CHARTS - MTOW CALCULATION (TEMPERATURE ENTRY) and not in TAKEOFF CHARTS - FLEXIBLE TAKEOFF (TEMPERATURE ENTRY) Am I supposed to use TOGA and use those low weight corrected speeds or can I use the lowest FLEX TEMP on the chart (FLEX TO) and the low weight corrected speeds?

Also consider:
1. TAKEOFF CHARTS - MTOW CALCULATION (TEMPERATURE ENTRY) PER-TOF-TOC-12-30 only considers the USE of TOGA.
2. PER-TOF-TOC-14-10 TAKEOFF CHARTS - FLEXIBLE TAKEOFF (TEMPERATURE ENTRY) CORRECTIONS PRODUCED ON THE RTOW CHART
first point says: "Enter the chart with wind and selected configuration. Interpolate for actual takeoff weight. Read flexible temperature associated with this weight.

"interpolate for actual takeoff weight" We can't because the weight is not on the chart (is actually Lower than the ones displayed). That would be EXTRAPOLATION.

please reference all your answers. Thank you!

[Cough]

Not current on type so can't answer as I haven't any manuals. But if you did indicate the aircraft type I'm sure that would help those who can.

[piratepete]

This is an issue common to all types.Most Take off performance charts have a range that at the top end exceeds the structural limit weight, and at the lower end often has a lower limit that often can be higher than an operating weight with little or no payload, ferry flights for example.
Some companies simply say "use the lowest chart weight " for a specific runway if your ACTUAL weight is lower than the chart, however these speeds might then be significantly higher than FCOM speeds for the actual weight.Obviously performance (engine out0 is not an issue but it is quite acceptable to refer to the FCOM/QRH to obtain the correct speeds for your actual weight on the day, as this has the effect of avoiding a deliberate "overspeeding" during the time on the runway.Pete.

[john_tullamarine]

I'd be more concerned about the potential for getting needlessly near to Vmc for the day.

Simple fix .. if the runway chart gives a speed schedule for a higher weight, it isn't going to present a major problem on the day ? Let's not be ridiculous but I would certainly like to have a suitable crosswind pad, based on the typical numbers, so that the speed schedule used is known to be above the book Vmcg numbers.

Keep in mind that the published speed schedules usually are based on nil crosswind (7 kt for the older BCAR manuals) .. the actual Vmcg will go up by, typically, 0.5kt/kt (fuselage engine twins) and a bit over 1kt/kt crosswind for quads .. if the wind happens to be from the wrong side when the noise quits on one.

[FE Hoppy]

Just be careful if your aircraft wants to fly before your V1/R speed. Had this once on a ferry flight and the chap at the wheel decided to put it back on the runway as we were still 10kt below the none weight related V1/R speed. It resulted in the aircraft deploying ground spoilers!!!

[vilas]

flavioromero12
The highest Flex at the bottom is regulatory limit of 25%/40% reduction. So keep the flex and only apply speed corrections at the bottom 1kt/T subject to minimum and check VMU limitation. You want to be conservative you can use the both the highest flex and speeds. No requirement of TOGA takeoff.

[flavioromero12]

Thank you all for the answers. Vilas, that is how I have been doing it. However the doubt arises when checking that extrapolation is only mentioned on MTOW section and not with FLEX TEMP method. in addition to not being able to proceed as per STEP number 1 that says: "Interpolate for actual takeoff weight. Read flexible temperature associated with this weight." that weight is not on the chart, so we can't really "interpolate".
I know the easiest way is to read the highest FLEX TEMP and use those speeds assuming a heavier weight.

[piratepete]

Dont confuse SPEEDS with THRUST settings.This discussion is about TAKE OFF speeds.Okay here is a problem for you.Due to whatever reason you must divert to XXXX.You have no runway analysis, your OPS department cant be contacted, but you must depart NOW.Where do you get your speeds from? FCOM? QRH? The runway is 13000 feet long, so performance most likely isnt an issue as the ocean is off the runway end, no obstacles.This has happened to me several times in a big jet.

[john_tullamarine]

Just be careful if your aircraft wants to fly before your V1/R speed.

Hence my observation Let's not be ridiculous. It should be obvious where the speeds become Vmc limited .. so, for Vmcg, one only wants a pad sufficient to cover Vmcg plus the likely crosswind increase in Vmcg.

This has happened to me several times in a big jet.

First, my view would be to delay the departure unless you have the AFM on board and can do some sums yourself.

The limit will then become the WAT data, which should be in the Ops Manual if you don't have the AFM. In addition, I would want to check that the runway slope doesn't present a problem with respect to first segment gradient, should that segment exist for the particular aircraft and conditions.

If the runway length clearly is non-limiting, in a similar vein to having a speed pad, I would be inclining to a reduced thrust takeoff unless there were some other reason suggesting not to do that, for example, an expectation of wind shear.

[piratepete]

Thanks John, yes as usual you are technically correct, and every situation will be different, with lots of variables, but after around 14,000 hours on one type , and this is not a technical argument, most pilots will have an idea whether it is SAFE or not to proceed with a given situation, not having full verified data.However as always this exposes you to possible litigation if anything goes wrong.....or worse.I have been forced into making such a decision three times so far in a very big jet.

[vilas]

I don't understand what's the complication. No matter where you land you always have FCOM and the Quick Reference tables will give you completely legitimate calculations. VMCG is also given. If you have RTOW chart the procedure is straight forward. The minimum speeds at the bottom take care of VMCG etc.

[MD83FO]

just ran it on flysmart on a generic 4000m runway at the lowest possible weight and sea level ISA

37 Tons
1+f
F69
V1 120
VR 120
V2 123
LIM-VMCG

TOGA
V1 118
VR 120
V2 127
LIM-VMCA

[john_tullamarine]

The minimum speeds at the bottom take care of VMCG etc.

Careful - there be dragons in the details ...

Vmcg is defined for nil (cross) wind (7kts in the old UK standards). Have a think what crosswind does to the aircraft's tracking ability .. think weathercocking.

For, say, a four-engined aircraft in a 30kt crosswind, and with a critical failure on the outboard engine on the windward side .. you might find yourself with an on-the-day increase in the book Vmcg by 30-40 kts .. ergo .. in the grass you go. Probably a matter worth considering in the case where you really don't need to use that very low speed schedule eg ferry, long runway, strong wind ...

If you don't have the flexibility to increase the schedule .. do you really need to go, right now, and bet that you don't have a failure on the "wrong" side ? Maybe you could delay until the wind abates a bit ?

[vilas]

The OP is about theoretical method. Practically I had suggested leaving it at Highest flex speeds which are higher than minimum.

[john_tullamarine]

Apologies .. not specifically criticising your post at all .. more a comment of general application to very low weight operations.

At one operator, for which I did some contract training years ago, the deal was to use the book figures without much thought for the infrequent ferry operation. A few sim failures in the appropriate circumstances raised more than a few eyebrows as the visuals pirouetted away into the grass ..