Mental math calculations in the cockpit?

[RM7599]

I was just curious as to what kind of mental math calculations are performed in the cockpits of the airlines.....regional and major. Just how difficult are they, and do you have to be a math wizard to perform them. Also, does the FMS system take a lot of the math work out of it. What is the most difficult calculation that must be performed in ones head? Any examples would be greatly appreciated! Thanks!

 

[bobbysamd]

Mental math

A couple we used at FSI in our Alitalia program: Point at which to begin decent, multiplying altitude times 3.

Same point to begin a non-precision approach using a three-degree glide. Example: If your minimum altitude on the intermediate segment of the approach is 1000 feet you begin your decent three miles out. Alitalia's philosophy was to fly ALL approaches with a three-degree glideslope because chopping and dropping and holding altitude in a DC-9 wasted fuel.

Vertical velocity to hold the 3-degree glide: Divide ground speed by two or multiply it times five. E.g., 100 kts = 500 fpm. You would know the pitch, power and trim settings you needed to achieve that performance. Worked like a charm!

PS-Set it up on your whiz wheel. Put the 30 over the 60 index, look for your 100 kts on the bottom scale, and look up to see 50, representing 500. I realize that it is not "mental" math, but it's easy.

 

[RM7599]

Yeah, I actually have that book, but most people I talk to say that most of what is in that book is rarely used. Obviously the enroute descents and a few others are used but how often do you actually use fuel dump......and a few other like that.

 

[eriknorth]

Wait a second...that there flying stuff involves math? I thought you just drove the dern thing like a car! I can only count so high, you know.

 

[BigFlyr]

If you can multiply by 3 for your 3 to 1 ratios in figuring descent points or crossing restrictions, that's all you'll probably ever use. Don't think for a minute that the FMS makes things any easier... you still have to back it up to make sure its doing what its supposed to... so now you're doing twice the work! The next time someone pulls out a whiz-wheel...

 

[Fr8DoggyStyle]

Not actually DURING flying but i use mental math for converting pounds to gallons to order fuel.

Take the pounds, drop the last digit and set that number aside in your head. Then split that number in half and and add the 2 up. Its within a couple gallons.

Example:

2000 lbs

Drop zero- 200

200/ 2= 100

200+100=300

300 gallons is equal to 2000 pounds

As a proof of concept 300 gallons times 6.7 (average spec. gravity for jet-a) equals 2010 lbs.

 

[Fr8DoggyStyle]

I forgot to mention- In most airplanes with single point refueling you dont really need to use that calculation. The fueling control panel shuts it off automatically at the set pounds.

 

[profile]

Still calculate pounds to gallons from time to time even with the widebodies, but not the way you to it. 1.5 x pounds = gallons at 6.7/gallon.

 

[Eagleflip]

And don't forget the easy way to convert degrees C to degrees F:

((Celsius temp X 2) - 5%) + 32.

For example, 20 C converted to degrees F is:

20 x 2 = 40

40 - 5%, in this case 40 - 4 = 36

36 + 32 = 68 degrees F.

This impresses the heck out of your passengers (or boxes, as the case may be...)

Or, you can just make it up as you do your PA...

 

[profile]

That's the best way, except that you subtract 10%, not 5, which, incidentally, you did in your problem (5% of 40 is 2, not 4). Works with negative temps too, just keep in mind that your "subtraction" in this case is going the other way.

-40C x 2 = -80, -(|80|-8)= -72, -72 +32= -40F

 

[tarp]

CA: We dutied off at 11:45 last night right?
FO: Yep, actually it was 11:48.
CA: And we dutied on at 0800, right?
FO: Yep.
CA: So was that reduced rest? Are we contract legal? Do we have compensatory rest coming? When do we duty off today?
FO: Standby. Let me try to work this all out.

Now there's some tough math questions!

I spend far more brain cells working on Timesheets, Crew Rest and Schedules than I ever will figuring temperature, descent rates or the occasional fuel in gallons vs. pounds.

 

[skyboat]

BigFlyr is correct-

As soon as you rely on the FMS some knuckelhead will come along and program a 6 degree glidepath into the thing and before you know it you're almost doing an emergency descent to meet a crossing restriction. I've never actually seen this happen, but i've heard about it....

The FMS is a great tool but I'm sure that there are countless stories of violations and accidents because the technology did not do what the operators thought it was going to do.

 

[BigFlyr]

Skyboat,

It happens all the time... Especially in the 737-800 which does not like to slow down and go down! You need to program the box quickly and correctly... then execute... then do the mental math to see if its going to work or not. If you get the dreaded "Drag Required" message... you might as well go to vertical speed mode and go for the barber pole!

 

[Crusty]

You go out to dinner with your crew. As the Captain you are presented the check. You have your F/O and five F/A's, and you all have the same thing. Everyone tosses in their "share" of the $105.21 tab to include the tip. How much will your share be???

($105.21 + 15%) / 7 x 2. You end up paying $35.00 for your hamburger and two lagers. Works every time.

 

[RM7599]

So, if I'm seeing this right, there is not so much mental math in the cockpit.......I get the point, especially from the last few replies!! Thanks for all the great replies, and if anyone has any real world examples, I would like to see them......besides splitting the bar tap

 

[Eagleflip]

Whoops, you are correct Profile--it is 10%....


I suffer from math lysdixia....duh!

 

[alimaui]

Okay very important mental math problem here (NOT!) but interesting....

Most of the time we descend gradually...on an ILS 3deg but for those of you who land so hard it feels like you are dropping out of the sky here is how you can figure out "how far you were dropped from"

*since no "square" sign anything squared will be shown as sq. ie Vsquared will be shown as Vsq


H=Vsq/231580

Where V=vertical speed in ft/min
H=Height in feet from which the aircraft could be dropped from to create the same intensity of touchdown

To Derive

V Finalsq=V initialsq + 2ad

Where V Final = Touchdown speed
V Initial = Zero (dropped from still)
a = acceleration (9.81 meters/second sq)
d = height (h) we are solving for


Have fun....

Ali