Motion Lotion: What’s the Commotion?

“The only time you can have too much fuel is when you’re on fire.” –Anonymous Pilot

Those are words to live by, in the flying business–but jet fuel is expensive. In fact, it’s just about the largest expense in the operation of the airline, which is why it makes sense to use fuel as sparingly but sensibly as possible. But as a passenger, what’s it to you?

Well, for starters, this:

tstm day

Do we go around it? Above it? Through? You won’t like the last option, but fuel is the double-edged sword in this fight: more means we’re heavier, which limits our climb. Plus, going around the weather will burn more fuel, limiting our options at our destination:

fms crz

We’re at 36,000 feet now, which is just about the optimum altitude. “Optimum” is a moving target: as you burn off fuel enroute, the jet gets lighter and the wing can handle a higher altitude, which means the engines can operate at a lower thrust setting, thus saving fuel. We’re within 200 feet of the max if we climb to 38,000 feet to top the weather. We can wait till the “max” readout shows “380,” or really, from experience, we know that in the time it takes to request and receive the clearance, plus what we’ll burn in the climb, we’ll be at the correct weight. But, there’s always a catch.


The airspeed tape on the left shows us a very narrow operating range at the top end of our altitude capability. That is, your range of acceptable airspeed is from about 212 to about 245. The “chain” above that shows the area of high speed buffet, meaning parts of the aircraft, above that speed, will begin to go supersonic. More importantly, though, in my mind, is Mach tuck: swept-wing jets tend toward a pitch down near the high speed limit, and guess what a pitch down does: your high speed becomes even higher. In a jet, particularly a passenger jet, if you don’t recover aggressively and immediately, you will not be able to stop what will become a dive.

On the bottom of the tape is the yellow line we call “the hook,” which is the slow speed stall. If you go below that speed, your airfoil will stall, and you will fall.

PFD coffin corner

So, at 38,000 feet, we have very little margin between the high and low speed buffet, requiring extreme vigilance on our part: turbulence, mountain wave action, or a drastic updraft of any kind can push us beyond either speed limit. Which is also part of the balancing act the captain must perform:

pfd coffin corner 2

I insert a slower Mach number in order to cruise more toward the middle of the range between the high and low speed limits. That, too, though, will affect our arrival time, won’t it? But that’s a balance I feel can be maintained, knowing that we’ve picked up some direct routing already. I’d rather sacrifice some time (and really, fuel) to gain a better pad between any adverse effects (mountain wave, thunderstorm up drafts, windshear, clear air turbulence) that could push us into either boundary.

And, I’ve already checked: the winds at the higher altitude are more favorable. To be even more accurate, I’ve requested a data-linked update to our flight management system, updating the projected winds the computer is using to calculate the times, distances and fuel burn it displays because what we data-linked into the system on preflight hours ago may not still be accurate:

fms crz wind update

The photo makes it hard to see, but the new, uplinked wind speeds are highlighted, all I need to do is push the “EXC” (execute) button and the entire nav calculation will be updated in a matter of seconds.

Climbing early has taken us out of more headwind earlier, so I believe the ETA will be largely unaffected. This hunch is borne out as we progress in our flight:

flt prog 1

We cross Pocatello, Idaho (PIH) six minutes ahead of schedule and up 700 pounds on fuel. If, however, the higher altitude winds were less favorable, we’d end up with the same result by going around the weather (more miles at regular cruise Mach)  as by climbing above the weather (less miles at a slower speed). The latter option is better, fuel-wise, as you can see from the fuel log above. But we’ll do whatever is safest and most optimum first, and worry about timing  later. Plus, if we don’t have what I consider a comfortable high speed-low speed margin at the higher altitude–we’re not climbing, we’ll just have to fly the additional miles (and minutes) around the storm.

It’s not just air miles between us and Seattle–it’s a constant balancing act of time, fuel, altitude and route. It all goes on steadily, quietly but relentlessly in the cockpit, but we all share the payoff in the end.



30 Responses to “Motion Lotion: What’s the Commotion?”

  1. Randy Sohn Says:

    Chuckle, now I wonder who teaches all that stuff in “How to be a pilot” ground school?

    • Nobody–as you know, it’s mostly as a result of “I’ll never do that again” personal experience that scared the crap out of you once, but never again!

      • Randy Sohn Says:

        Well, I sure dunno, thinking tho about what Dux says about both Boeing and Airbus wondering where they’ll ever get enough pilots to crew all the coming airliners.

      • Yes, it’s a mad scramble now to gin up flight training, because all of our furloughed AA pilots have either accepted recall or given up their recall rights. Hard to believe that ten year furlough nightmare is over.

        Supposed to start interviewing pilots in September for new hire classes in January.

  2. Sounds great, but seriously. Am I going to make my connection?

    Ha ha

  3. Tini von Allwoerden Says:

    thanks for the insight xx

  4. Chris, it looks like the “anonymous pilot” who commented on fuel and fire was Ernie Gann. Look here:


  5. Tom Barnes Says:

    I take it that it’s your own paper clip and rubber band document retention system above the FMS?

    I’m sure Boeing could make those available as a factory option, but probably at a lot more cost…

  6. Tim Perkins Says:

    I wonder what percentage of your passengers equate piloting a 737 to driving a car…that pretty all you and FO are doing is steering, accelerating, and braking.

  7. I love the aviation, thanks for this blog!!

  8. Cedarglen Says:

    A wonderful post, Chris – ands you know there will be questions.. In this case, I guess you are both Captain and PF. If the other seat was flying and briefed a slightly different but reasonable plan, would you reject it, modify it or accept it. If ‘tight-brain’ correction is necessary, would you do it 1) before take off, 2)inflight, or 3) after landing?
    While you are *always* the PIC, and you may drive your airplane at will, I’m curious; when your FO/partner is allowed to fly, does s/he enjoy the same degree of independent thought to create and brief a taxi, takeoff and flight plan? If you have (any) issues with the FO’s plan or briefing, are they discussed (resolved) and understood before the aircraft moves? In your airplane, are both pilots fully satisfied with the pending program – and before the wheels turn?
    With apologies as necessary, Chris, I don’t sense that degree of “CMR,” in today’s post. I’ve read much better CRM-focused posts from your fingers and, perhaps, I’m missing something that was implied. Does the FO (I’ll assume PF in this case, but applies to any function) do his/her own, independent time/fuel/hold calculations – and then compare with your and those of your (two, I understand)FMCs? In the end, I don’t think this post reflects your professional actions in a situation the includes a difference of opinion among pilots. I don’t see that here and I wonder. Ordering when necessary is fine, but it should still include input from your FO, especially of s/he is the PF. Am I missing something? Darn good post -C.

    • No, that’s not how it works. Before the crew even shows up at the jet, the captain has agreed with the route and approved the fuel load. Never have seen a First Officer involved in that process, nor was I involved that way as an F/O.

      So, no, the F/O doesn’t “brief a different plan” for the flight on which he’s doing the flying. In fact, all of the briefing on the ground is done by the Pilot In Command, which at all times is the captain. Again, I never had a problem with that as F/O.

      In fact, I felt pretty comfortable with my position as F/O: my job was to offer my best advice, then follow through with the captain’s course, again, giving my best input. Certainly, anything I thought was unwise or unsafe, I’d speak up immediately. As captain, I expect the same.

      So if I’m not comfortable with a 330 knot climb out (that presumes smooth air, very rare) I’ll tell the F/O, “How about 280 in case of bumps?” And he’ll slow. If I’m not comfortable with the cruise Mach being too close to either limit as I described in the post, I’ll say, “Let’s split the difference between the limits” (and I’d do the same if he suggested it–although I always do anyway), and he’ll input a different Mach–or I will myself.

      On the F/O’s leg, if he says “I’d like to go left around the weather,” I’ll agree if I think it’s a good idea. If not, I’ll say so: “Left is going to put us downwind. How about right?” Because if there’s a consequence to his preference I’m not comfortable with, that’s the captain’s responsibility to decide otherwise.

      I’d also take the same advice as captain–if I say, “I’m going to go through that gap” and the F/O says, “I’m not comfortable with that,” I’d say to myself “this guy’s instinct is important–we will go around this cell, rather than between cells.”

      As far as fuel calculations, no, the F/O doesn’t work out his own plan. He just works with the agreed upon flight plan. If there’s a difference of opinion, there’s no “vote” or delegation of authority from the PIC (pilot in command) to the PF (pilot flying). As F/O, you offer your best advice, then press on with the captain’s decision. As captain, you weigh the advice carefully, then make the best choice possible.

      That’s CRM and the FARs. The F/O doesn’t become the captain on his leg as PF.The smart captain always carefully solicits and incorporates the best advice he gets. But ultimately, there’s only one PIC on every crew, every flight.

      I remember one dark and stormy night when I was a DC-10 F/O and we were in a difficult situation. I’d given my best advice (the flight engineer had too) to the captain, then it was time for him to decide what to do. He said to me, “This is a tough decision,” and I sensed him almost wanting me to make it. I just answered, “Yeah, I bet it is.”

      That’s why the captain “gets paid the big bucks.” The responsibility, and therefore all the authority, belongs to the captain.

  9. Perhaps a dumb question, but you mention updating the data link to your flight management system in order to update the winds the computer will use to calculate times, etc…how long has this type of technology existed in the cockpit? And what happened in the earlier days of flight, before computers could crunch all of this?
    Did you just have to build in bigger margins (more fuel, more time), or was there more to it?

    • I’m not really sure when the wind update data link came into use–I was on the MD-80 pretty much from 1991 to 2010, and they sure didn’t have that capability. In fact, they couldn’t data-link upload anything: the flight plan had to be manually entered, point by point.

      Average winds, based on historical data, were used for planning. That required more fuel, which was the price of doing business. But with fuel being such a huge expense, state-of-the-art aerodynamics, Flight Management and Navigation systems, and jet engines are absolutely mandatory to fly a competitive airline. Which is why American is in the midst of the largest re-fleeting process in history: new 737-800s, A-319/320s (crews in training, revenue flights start in September), 777-300s (in service now flying long-haul), and 787s coming next year.

  10. I presume your airspeed range at 41000 feet is 212 to about 245 meters/sec and not knots. Do you normally have the airspeed shown as m/s rather than knots?

  11. Captain,
    Yours is my new favorite blog. Keep up the great work. It’s very enlightening to see the world of aviation through experienced eyes.

  12. The way you explain weight and altitude considerations makes sense, yet the narrow range of acceptable airspeed was a real eye-opener to me. It adds new meaning and a hint of the complexity to the term “flight management” for a non-aviator. Thanks.

  13. clementinegoesusa Says:

    That was profoundly un-enlightening. But cool to read, anyway.

    • You’re a better man than I, or maybe you just have too much time on your hands: if I start reading anything, if it’s profoundly unenlightening, I find something else to read.

      • clementinegoesusa Says:

        I’m actually a woman, maybe that explains everything. Also, I didn’t mean it in an offensive way. It was a humorous way of saying “wow, piloting is supercomplicated”, but I suppose humor is not for mathematical brains.

      • Guess we’re both making assumptions that aren’t quite accurate: I’ve been banished from the homework helper status by my junior high student daughter, after helping her with fifth grade math–and she got a 65 on the assignment.

        Mathematical my brain is not, although sometimes I wish it was. I do have a doctorate in English, which would never have been conferred if they suspected I had any mathematical aptitude. Bad karma for the entire discipline.

  14. Can you comment on the possible reason for the Asiana accident in SFO? Very scary

    • No, I wouldn’t want to speculate. The NTSB has the flight data recorders, the cockpit voice recorders, the pilots and most of the jet. We’ll get factual answers in due time.

      • The saddest thing I’m taking out of this so far is the unsubstantiated story of the passenger surviving the crash but getting hit by a rescue vehicle.

  15. John Brown - Private Charter Flights Provider in USA Says:

    Hi Chris! Wonderful post.

    It’s true that pilots have a thankless life. There are so many aspects that they have to keep in mind to ensure safety and security of passengers. There is a constant battle that takes place with the weather, clouds, and one’s own mind (often tired by the long schedules).

    Keeping that aside pilots have to focus. Lives of so many passengers are in his hand. He needs to be steady. Be optimistic always. Because it’s him that everyone trusts. Passengers believe they will be safe throughout the journey because there is someone taking care of them. There are so many things that crosses the mind of a pilot be it for commercial flights or private charter flights.

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