"Air Shuttle 7372, maintain best forward speed"

A FedEx MD-11, east bound two thousand feet above us.

And now the story of how I chose my blog's title.

Disclaimer: Lengthy, and contains scientific content!

But first, some background:

All of the airlines have different callsigns used when communicating with ATC; some are pretty obvious, like United, and Southwest, while others are a bit tougher to link to the airline, such as Redwood, Brickyard, or Jetlink. We are Air Shuttle. The call sign is then followed by the flight number, typically 4 digits for the regional carriers, and anywhere from 1 to 4 digits for the mainline carriers. But enough about callsigns, for now.

Pilots have limitations on how many hours they can fly in certain amounts of time. Your typical commercial airline pilot is limited to 1000 hours per year, 100 hours per month, 30 hours per 7 days, and 8 hours a day (scheduled). Without getting too complicated, you cannot be scheduled to exceed these times. However, if you encounter delays throughout the day, it's not like you just become a vegetable up front when the clock hits 8 hours for that day. Legal to start, legal to finish, as they say. So our schedulers won't (intentionally) schedule us to exceed these times, but if we encounter delays then there can be conflict.

Conflict is known as "timing out". And that's exactly what my Captain was going to do after one of my first trips. We had flown more hours than we were scheduled for, and he was going to exceed the 30hrs/7days if he went to work as scheduled the day after my trip with him ended. Good news for him; this means he gets the day off because he can't legally fly.

It was on our last leg of the day, going home (for him) that he told me he was going to be on the border line of timing out, based on our estimated time of arrival that our computers were projecting.

Another sidenote, and I'll try to keep this simple as well: At lower altitudes we fly at certain airspeeds, in knots, or nautical miles per hour. As we climb higher and higher into the atmosphere, due to the density changes, we have to start paying attention to our Mach number instead of knots. The Mach number is the ratio or our speed versus the speed of sound. Mach 1.00, is the speed of sound, and you would be right at the "sound barrier", but that's a whole 'nother topic.. Because of how the wings are designed and how lift is created, air is actually accelerated over the wings during flight, and thus travels faster than the airplane is actually going. We can't have any airflow around the airplane exceeding mach 1, so we have established critical mach numbers (max speed) as well as profiles which include a climb mach number, and cruise mach number.

Hopefully you're still with me...

We typically cruise at Mach .77 (77% of the speed of sound) in the -700/-900 and Mach .74 (74% of the speed of sound) in the -200. So there we were, cruising at M.77 at thirty something thousand feet, when my Captain says "hey, I'm going to be close to timing out, slow it up a little". Now, I must also add that we were in fact running ahead of schedule, and would not have slowed down if it would cause the pax (passengers) to be late. Also, slower cruising speeds (to a certain point) use less fuel, and save the company money!

So I pulled it back to M.74... and less than five minutes later, ATC says :

ATC- "Air Shuttle 7372, say Mach number"
Us- "Shuttle 7372 is doing M.74"
ATC- "Roger, Air Shuttle 7372, maintain best forward speed for spacing into Chicago O'hare"

Doh! There went the Captain's plan. Fortunately for him, and unfortunately for the pax, we had to hold for 15 minutes outside of Chicago due to weather when we got closer. The pax were late (but not our fault!) and my Captain timed out.

And there you have it, how Best Forward Speed came to be.