Boeing 80 knot call v Airbus 100 knots. Why the difference.

[Centaurus]

For the B737 series the 80 knot call during the take off run is SOP. Considering VR depends on flap setting and could be up around 150 knots on occasions, 80 knots seems a relatively low speed, when defining the line in the sand between low energy and high energy.

On the other hand,I believe some Airbus types have a 100 knot call - presumably for the same reason that Boeing go for 80 knots. Again VR can be also be 150 knots plus or minus here and there.

With both manufacturers, recommended crew actions may change in event of a non-normal event showing up before or after 80 knots Boeing, or 100 knots Airbus. Both speeds are well below a typical V1.

Is Boeing too conservative in selecting the lower figure of 80 knots compared to 100 knots of Airbus? I would have thought that 100 knots was a more realistic decision point (and that already has plenty of fat built in) for the line between low and high energy stops?

[Denti]

I guess the figure was introduced at some point and not changed much over the years. However as you can use V1 as low as 100kts on some 737 models it actually makes sense to use an 80kts call.

[muduckace]

Is Boeing too conservative in selecting the lower figure of 80 knots compared to 100 knots of Airbus?

80 knots has been proven as as effective A/S by Boeing (and MDC products) for an efficent A/S for cross check. I do not see this as a conservative limit as 80 kts is plenty of pitot pressure. If a pitot tube is clogged by degridation or outside influences such as a muddober nest it would certainly show prior to 80 kts.

Seems to me that airbus loves to sell their products closer to their limitations to make the ignorant number crunchers that rule the skies happy.

[By George]

On the 747, 80 knots is the low speed decision to abort for any EICAS message. Above 80 the only reason to abort is the usual engine failure, unsafe to fly decision before V1. Above 50 knots the A/T goes from THR REF to HOLD were the auto throttle servos are inhibited. This aunnunciates around 70 knots. With the average VMCG around 118 knots a 100 knot check would seem a little late in my opinion. From memory both the 737 and the 727 also had the 80 knot call.

[hetfield]

Yes we changed from 80 to 100kts in our compamy as well some years ago. On BOEINGS and AIRBUS.

AFAIK the reason was the so called high energy regime which starts per SOP definition with 100kt. So the 100 call is for

- ASI check
- incapacitation check
- high energy awareness

[skyloone]

An early ok

For our company ops, (73 drivers) 80kts has go/no go implications, is an early incapacitation check and also a check on the FMA's to see that Thrust Hold is active. Also I suppose that 80kts for us is far enough away from Contaminated V1 to not clutter that 'time space' approaching V1.

[Checkboard]

If you have a look at the brake energy charts, aborts below 80 knots usually don't have any hold over cooling requirement. An abort at 100 knots might see you shutting down for 30 minutes before attempting the next take-off.

[Old Smokey]

Boeing aircraft have "Master Caution Inhibit" activated just above 80 knots. (I cannot recall the exact figure, somewhere in the 83-87 Kt range).

Energy management for a potential RTO is, of course, the major issue. As a secondary, but important issue, the 80 Kt call is the 'last chance' to observe a Caution which may develop further into a larger problem.

Regards,

Old Smokey

[Dan Winterland]

So do Airbus.

I suspect the diference is due to the fact they had to be different, So they chose 100 instead of 80. Both seem arbitary figures.

[catiamonkey]

V1, of course, is the certified speed for which you have limitations. There's no certification basis of 80 or 100. I seem to recall a line about it in the AI FCOM or FCTM that, for the purposes of RTO, 100 kts is a arbitrary figure.

The A300-B2's airspeed indicator is missing the 80 mark, so it seems Airbus came up with 100 kts 40 years ago.

[square leg]

brake efficiency?

Maybe one other reason are steel brakes (less efficient) versus carbon brakes (more efficient) on the smaller models of B&A respectively when it comes to high energy stopping. Maybe the numbers were traditionally taken from past experience and applied across all models respectively.

Or are steel and carbon brakes equally efficient??

[despegue]

Eh Denti,
Are you sure about a V1 of 100kts?... Remember Vmcg?... it is around 116kts. on most models afaik. This is sadly not always depicted on performance charts.

[decurion]

I am currently writing a paper on high speed RTOs. I have looked at the different speeds used by Boeing and Airbus (80 versus 100 kts). First these numbers are not certified. Other manufactures have given others numbers like 70 kts.


I believe the 80 kts from Boeing originates from the Takeoff Safety Training Aid (1993). However I am not 100% sure about that.

Airbus gives the following background info on their 100 kts. value.
The statistics and experience have shown that, as soon as the aircraft reaches 100 knots, the safest course of action is for the flight crew to continue the takeoff, unless a major failure or a serious situation occurs.

The takeoff roll is divided into a low and high speed segment. If the aircraft speed is less than 100 knots, the aircraft is considered to be in the low speed segment and an RTO decision leads to a low risk maneuver. If the aircraft speed is above 100 knots, the aircraft is considered to be in the high speed segment and an RTO decision may potentially involve more risks. The speed of 100 kt was chosen to help the captain make his/her decision and avoid unnecessary RTOs at high speeds.
See: www.skybrary.aero/bookshelf/books/197.pdf

Also note that autobrakes often don’t work at the lower speeds during an RTO.

[TheWanderer]

Originally Posted by despegue

Eh Denti,
Are you sure about a V1 of 100kts?... Remember Vmcg?... it is around 116kts. on most models afaik. This is sadly not always depicted on performance charts.

Vmcg is not a static value but changes with engine rating and air density (temperature&pressure altitude).
On most B737, 118 kt sounds familiar as it is a conservative value (actually the max Vmcg for a 22k engined aircraft) that was put in the QRH by Boeing.
If you look to the actual Vmcg charts in the performance manual, you will find also other values, especially lower Vmcg at higher temperatures and/or lower engine ratings.

For example a B737-300 with 22k engines installed has a Vmcg between 94-118 kts, while the same aircraft with 20k engines has a Vmcg between 94-113 kts, depending on temperature and airport elevation. (Values are taken from B737-300 FPPM)

[Denti]

Yup, im sure about that. Got a V1 of 104 from our boeing performance tool lately for a takeoff on contaminated runway (slush, 3mm), crosschecked it with a Vmcg chart and our Vmcg was around 98kts or so, -700, derate 2 (18,5k) at sealevel pressure and something like 0°C.

Vmcg varies a lot depending on model and selected thrust setting, quite a nice thing during winter ops to be able to reduce V1 by a lot if necessary.

[blousky]

Also, "eighty knots" is much quicker to say than "one hundred knots".
Maybe the French say it as "Cent Noeuds", which in turn is easier than "quatre-vingts Noeuds".
Being relatively arbitrary figures, they may have chosen those that sounds better?

[Human Factor]

Yes we changed from 80 to 100kts in our compamy as well some years ago. On BOEINGS and AIRBUS.

To throw a further spanner in the works (and deliberately not wanting to creep the thread into Big Airways vs Rest of the World), Big Airways use 80kts for both Airbus and Boeing!

[hetfield]

Yeah, and L arge H ub feeders use 100.

[alexban]

hetfield , did you get an approval from Boeing when changing their 80kt recommended speed to 100kt , or did you announce them about the change?
If something would happen, one reject at 95 kt for a reason included in 'before 80kt ' , and leave the rwy , would it have any implications regarding inssurance ,for ex,?
I'm asking this cause we had some discussions regarding commonality with Bus fleet on calls..

[Ginetta]

On the A320 series (dont't know about 330/340), 100Kts is also the speed that the wind readout first appears on the ND.
From the LHS, scanning across from PFD ASI to Stby ASI, it's quite easy to include this data.