Time To Station Question (on Commercial written)

[BrettInLJ]

I'm a little confused on some math and visualiztion required for a time-to-station question in the commercial written test pool.

I understand the formula that if you are flying at a certain angle past a station that the time to station can be calculates as:

Time to station. = 60 * minutes flown between bearing change / degrees of bearing change

Now the question reads along the lines that if you maintain a constant heading, the relative bearing of 10 deg. doubles in 5 minutes. What is the time to the station? So I interpret this as a 10 deg. bearing change (doubling from 10 to 20 degrees) in 5 minutes.

Time to station = 60 * 5 / 10 = 30 minutes

But its wrong! Because there is a rule that if the relative bearing doubles than the time to station is equal to the time of the relative bearing doubling. So the time to station is 5 minutes, which makes sense using common sense. How can the above equation be right for other bearing changes, but not work in this case? Can a more mathematically inclined person explain this to me please.

[MidlifeFlyer]

[ QUOTE ]
I'm a little confused on some math and visualiztion required for a time-to-station question in the commercial written test pool.

[/ QUOTE ]memorize the formula they give you or memorize the answer to the questions. Don't worry about it. It's one of the single most useless calculation in all of modern aviation:

if you intentionally go off course for 10 minutes you'll be able to calculate that if you hadn't gone off course, you'd be home by now

[sorrygottarunway]

yeah...

apropo... has anyone ever done this, or used this calculation?

[blimpguy]

Yes, I have used this once...no wait, that was on a written exam.

The trick I use for these is to memorize the formula and write it down on the scratch paper as soon as your time starts on the test. No sense in wasting valuable mental real estate.

Good luck.

[mtsu_av8er]

[ QUOTE ]

has anyone ever done this, or used this calculation?

[/ QUOTE ]

Well, one time I was over Southwestern Arizona in a 152. I'd been flying for 3 hours, trying to make it Los Angeles (long story....zombies, rebellion . . . you name it, we had it). I knew that I was on the 219 Radial of PXR, but I couldn't see where. PHX TRACON was down, because of the zombies. Soviet missles had already knocked out the GPS satellites, and there were obviously already too many people using the DME on PXR - alas, no distance info!!

Ground reference was out of the question - after all, it was 200 OVC! And then I remembered my formula! Instantly, I knew exactly where I was!

So, never say never!!

[MidlifeFlyer]

[ QUOTE ]
and there were obviously already too many people using the DME on PXR

[/ QUOTE ]ROTFL!

[250blue]

Flight service actually uses this when they are helping a lost pilot to do a "DF Steer" (I don't see where it is useful for a pilot in flight though). When you key the mic, FSS can figure out what radial you are on from a VOR, then give you a heading to fly, time it, and figure out what radial and distance you are at. Got this info at the "tour" and thought "ah ha, there is a use for it, just not in the cockpit"

I believe the difference in the formulas you are refering to is dependent on your RB when you start the deviation. For example, if you are going direct to the station and turn 10 degrees and time, then when your RB (10) has doubled (20) then that is the time to the station.

However, to use the first formula you referred to you must turn 90 degrees to the station and time for a specific change in radial distance (ie. 10 degrees). In this case, your relative bearing never doubles (no wind condition) since you turn 90 degrees from the station to start your time.

[JDE]

[ QUOTE ]
apropo... has anyone ever done this, or used this calculation?

[/ QUOTE ]

My buddy told me yesterday that he had to do this...or distance to the station...or something, heck I don't remember. All my comment was..."You actually remembered that?" And his reply, "I only remember because I taught it to my student the week before."

[mtsu_av8er]

[ QUOTE ]
[ QUOTE ]
and there were obviously already too many people using the DME on PXR

[/ QUOTE ]ROTFL!

[/ QUOTE ]

I was hoping somebody would catch that . . .