MACH

Often, when we are flying, my wife will remark that we shouldn't worry about being late because the captain will just speed up the plane to make up time.  She's sure they do that.  Maybe she's right, I don't know.

It did make me wonder about airplane speed.  Here's what I found out.

The pilot-types talk in terms of "mach" which is the speed of sound.  I'll use the more familiar 'miles per hour' (mph) for you.  One mach is equal to 758 mph - you don't have to remember that.

So here's the deal.   Every plane has an optimum cruising speed at every elevation.  It's the way they are built and all planes are different.  It is the best utilization of fuel.  The weight they are carrying effects that a little bit but we won't worry about that. The newest planes have that speed adjustment built into them with auto-pilot. 

For instance, a Boeing 747 at 35,000' should be flown at 652 mph.   A Boeing 777 at 35,000' should be flown at 637 mph; a 757 at 606 mph, a 737 at 561.   Okay, you get the picture. 

Here's another thing to consider; all eastbound flights fly at an odd level, westbound fly at an even level.  That means that a plane from LA to Cincinnati might fly at 35,000' and one flying from Cincinnati to LA might fly at 34,000'.

Sometimes a 747 gets sent on the same path as a 777 ahead of it.  The 777 pilot flies at 637 mph.  Be assured, the 747 pilot is not allowed to pass him - he has to slow down and travel at the 777's speed.  His only alternative is to ask the air traffic controllers for a different elevation. 

That's all for today.  You now have something to talk to that attractive person sitting next to you on your next flight.