Maximum safe speed for a B767-200

[Townie88]

I recently travelled from Cuba to Manchester on a Boeing 767-200. We experienced particularly strong tailwinds (130-150 mph) and at one point the plane was travelling at a groundspeed 689 mph. Out of interest I was wondering what is the maximum speed this aeroplane can travel at before being under too much stress (as may have happened to the Air France airbus earlier this year), as I thought the fastest these planes could go is around 560 mph!

Also, does the amount of pressure the plane is under differ depending on whether it is travelling at these speeds due to being carried by a tailwind or is doing so at the command of the pilot (if it is even possible to reach these speeds purposefully!).

Thanks

[Townie88]

Forgot to say we were travelling between 35000-37000 ft if that makes any difference!

[BoeingBobby]

I recently travelled from Cuba to Manchester on a Boeing 767-200. We experienced particularly strong tailwinds (130-150 mph) and at one point the plane was travelling at a groundspeed 689 mph. Out of interest I was wondering what is the maximum speed this aeroplane can travel at before being under too much stress (as may have happened to the Air France airbus earlier this year), as I thought the fastest these planes could go is around 560 mph!

Also, does the amount of pressure the plane is under differ depending on whether it is travelling at these speeds due to being carried by a tailwind or is doing so at the command of the pilot (if it is even possible to reach these speeds purposefully!).

Thanks

This is a joke right?

[Townie88]

No its not a joke. Which part of it is funny?

I know nothing about aviation so I dont know if this is a stupid question but it definately was a groundspeed of 689mph (not kilometres ph) which I thought was odd - I dont know if this is different to airspeed?

[SYDCBRWOD]

No its not a joke. Which part of it is funny?

I know nothing about aviation so I dont know if this is a stupid question but it definately was a groundspeed of 689mph (not kilometres ph) which I thought was odd - I dont know if this is different to airspeed?

The reason why planes have limiting speeds is that if the airframe goes faster through the air than that speed the airframe may sustain damage. Note through the air (airspeed). Groundspeed is usually unrelated to airspeed because of winds. Lets say the figure you provided is correct at 560MPH, if you had a 500MPH tailwind you would have a groundspeed of 1060MPH, if the airplane was flyiing against the wind you would have a groundspeed of 60MPH. In both cases the airspeed (speed of the air over the wings would be the same 560MPH.

Some routes have prevailing winds that affect times - Going West toward Perth aircraft are still doing the same airspeed, but because of the headwinds their groundspeed is less - they take on more fuel, and the trip takes longer than the trip back East from Perth to say Sydney.

One of the pilots can probably provide more on this but VNe will vary with altitude too.

[MCM]

SYDCBRWOD has explained it very well. I'll try and go for the "intermediate" answer, and I'll leave the "advanced" answer to Gabriel... he manages to explain the in depth stuff rather well.

In terms of aircraft operating speeds, it is all dependant on airspeed. Airspeed is, basically, the speed the aircraft is passing through a body of air. There are maximum and minimum speeds the aircraft can operate, and yes, its only relative to the air around the aircraft.

So, if we then move that body of air while we are flying through it, we are changing our groundspeed... but the aircraft is still flying through the air at the same speed as before... so the airspeed hasn't changed. This allows us to take advantage of tailwinds... the aircraft is still doing its standard speed relative to the air, but the air is moving in the direction we are going, giving us a higher groundspeed.

Conversely, headwinds work against us. We are making our good standard speed through the air, but the air is moving the wrong way, making our progress relative to the ground a lot slower.

Now, when it comes to maximum speed changing relative to altitude, that is true. For the 767-300 (and I think the -200) the maximum speed is 360kts, or 0.86Mach (86% of the speed of sound), whichever is the lower. That is in Indicated airspeed, which is what pilots use... but its not the same as True airspeed, or the speed you are actually going through the air.

So, if the air isn't moving at all relative to the ground, then Groundspeed = True Airspeed = Indicated Airspeed x Correction factor. So, the maximum speed a 767 can fly in terms of groundspeed is Max Indicated Airspeed (360kts or 0.86M) x Correction Factor (to TAS), +/- headwind/tailwind.

So, just picking a figure for a max groundspeed is impossible .

I can make the situation worse by mentioning that the speed of sound varies with temperature, and as such varies with altitude. So, while the max speed at altitude is 0.86M, M has changed as you change altitude .

So, basically - unless you have access to the pilots instruments, you'll never know how close you are to the max speed

[Townie88]

Complicated stuff then! Thanks for your help

[Peter Kesternich]

Actually not that complicated. With AIRcraft the only kind of speed that really matters is AIRspeed