B767 Vmo/Mmo in UK
 

I think it was in the very early hours one morning in a bar somewhere I was told the 767 is limited to a speed below 360/.86 in the UK.

Is this the case? If so, why? If not, I guess I had a few too many rum+cokes.....


Cheers,
Kam

You are half correct re the UK;

767 360 kts IAS / 0.84 IMN
757 350 kts IAS / 0.84 IMN

Where do you fly and what are your limits? We all know the A/C are capable of higher figures as per Boeing specs. Other countries in Europe will use different (often higher) figures.

I operate out of Sydney Australia and we are limited to 360/.86.

Just out of interest, what would be the highest mach you would comfortably cruise at with the .84 limit? In smooth air I find with our A/Ts you have to keep a pretty close eye on the speed when cruising around .83.

Do you have any idea why the limites are lower in the UK ?

For your info for the B767:

FAA VMO 360 MMO 0.86
CAA VMO 360 MMO 0.84

The FAA requires that a margin of no less than .05 mach exist between Mc and Md. Md for the 767 is 0.91 so 0.91-0.05 = Mmo 0.86

The UK CAA requires that the margin between Mc and Md be sufficient for an encounter with a head-on gust. For the 767, a head-on gust would have a velocity of 45 feet per second EAS at Vmo/Mmo. This equates to a 0.07 Mach margin between Mc and Md therefore 0.91-0.07 = Mmo 0.84. This gust value is determined at an altitude of 25,000', the lowest altitude at which Mmo could be achieved. At higher cruising altitudes the max gust value would be lower.

In addition to the above the FAA and CAA have differing ways in specifying buffet limited altitudes. As the FAA have no specific requirement for manoeuvre margin to buffet Boeing have adopted 0.3g as the min manoeuvre margin. The calculation assumes a cg value of 25% MAC a typical airline in service CG. If the actual CG is fwd of 25% the margin will be slightly lower than 0.3g. The CAA require 0.3g but based on the more conservative CG of 7% MAC which thus results at average in service CGs, in a reduction of up to 1,000' in cruise altitude capability.

Here at RBA we operate both the B757 & B767, the former are under FAA regulations and the latter under CAA. There are a number of other small differences between the FAA and CAA but I hope you find the above of interest.

VH-KAM I operate out of London and our SOPS insist we use ECON in cruise, with 290/.78 in turbulance. ECON usually equates to M .8 in both the 757 & 767.

Expert I hope you are a trainer as that is a very good answer.

Thanks vnavspeed & yes, good guess!!

I assume you mean ECON with a sensible cost index!

Expert YES, could you email me with your email address?

A quick question for you guys, if you could email the answer, it would be fantastic. What is the Vref on a medium heavy 767 on a medium day? I got this answer from my nephew who thinks I know everything aviation related, only to find out that I don't.

Commander, we calculate Vref straight from flap setting and gross weight.

Max landing weight on the 767-300 is 145,150kgs, a typical mid landing weight would be around 125,000 - 130,000kgs, at which point the Vref30 (Vref at normal landing flap, flap 30) will be around 135kts.

To give you an idea Commander, at 100,000kgs Vref30 is 119kts, at 145,000kgs its 145kts.

I keep a 767 in turbulence at about .78, as per regulations. I have found that most British 767 operators (AIH, BAL, BAW, etc)will keep a normal cruise speed of .80, no more. In light turbulence it is kept at .79 but it doesn't make too much difference higher up. It's low altitudes like 290 - 330 that will worry me.

A VREF can go as high as about 179 with 190,000 kgs aboard, it all depends, but like the other one said, it's from 119 up and can really be varied.

I think that around our MTOW (185, 000) the Vref Flap 30 is artificially increased by a couple of knots ( to 175) to give extra manouvreing margin which leads to the situation where if you had to make a heavyweight landing around max T/O weight it would be slower at flap 25(168 kias at 185 000) using Vref Flap 25!!

To add to the above question what flap limit speeds do other operators have on their 767's. Our 767-300 a/c have a flap 1 of 250, and a flap 5 of 230, and flaps 15/20 of 210. This at high take off weights requires a close observation of speed so need to exceed flap limitation speeds. eg Vref30+80 @185 TOW is 255 knots where the limit speed is 250 and +40 is 215 and limit speed of 230.( we all know how long it takes to go flap 5 to flap 1 ) Can make an interesting departure in windy and stormy weather. I have heard that higher speeds are available for purchase from Boeing?

[This message has been edited by Speedbrake UP (edited 20 March 2001).]