Private Pilot Test Question #3550-1 Confusing

K

kevin7720

New Member
Hello, I am having problems working through this question and was wondering if anybody cared to walk me through it? I am using ASA Test Prep and can't seem to figure out where the True Airspeed Calculation is coming from.

3550-1. On a cross-country flight, point A is crossed at 1500 hours and the plan is to reach point B at 1530 hours. Use the following information to determine the indicated airspeed required to reach point B on schedule.

Distance between A and B.....70NM
Forecast wind...........310 at 15 kts
Pressure altitude................8,000ft
Ambient temperature.............-10C
True Course...........................270

The required indicated airspeed would be approximately

A-126 knots.
B-137 knots.
C-152 knots.

Answer

Thanks I have tried to work through the question but am not getting it through my thick skull. If someone can make sense of the question I would appreciate it. Thanks!:)
 
You have 30 minutes to cover 70 nm, which requires a groundspeed of 140 knots. The forecast wind of 310/15 yields about a 12 kt headwind, so you need a true airspeed of 152 kts to achieve that 140 knot groundspeed. At 8000' and -10 C, 152 ktas = 137 kts calibrated airspeed--which is as close to indicated airspeed as you can get with the information provided.

Is that what you're looking for? Or how to find all this with your E6B?
 
In the little window that says pressure altitude on your E6B.

Line up -10C and 8000 feet.

That gives you a figure of around 6200 feet Density Altitude.

You have a 12 kt headwind, so to cover 70nm in 30 minutes you will need a ground speed of 152 kts.

The True Airspeed of 152kts corrected for density altitude. (Outer Ring to inner ring on your E6B), gives you a True Airspeed of 139kts.

Since the E6B is not dead on balls perfect the closest answer is 137kts.

I hope that helps some.
 
desertdog71 said:
The True Airspeed of 152kts corrected for density altitude. (Outer Ring to inner ring on your E6B), gives you a True Airspeed of 139kts.
Click to expand...

Hahaha...I made that same mistake first time through. :insane: See if you can find the error.
 
Thanks that makes it crystal clear now!!! I was making the question much more difficult than I needed.

I am glad to have such a quick response and thanks for the help!

Kevin
 
And welcome to jetcareers!

The usual answer you'll get from me is "I remember when I used to know how to figure that out!" but there's always someone online that actually knows.
 
The scales change right at the 15 on both rings. One tick mark = .2, not .1--unlike the inner scale, where 1 tick mark is still = .1 I'm guessing you did the same as me and used the second tick mark after the 15 on the outer ring (154) instead of the first tick mark. Using the first tick mark, the KCAS is indeed 137 kts.
 
aloft said:
The scales change right at the 15 on both rings. One tick mark = .2, not .1--unlike the inner scale, where 1 tick mark is still = .1 I'm guessing you did the same as me and used the second tick mark after the 15 on the outer ring (154) instead of the first tick mark. Using the first tick mark, the KCAS is indeed 137 kts.
Click to expand...

See I learned something today, I was totally unaware of a change in the scale.
 
Remember those FAA questions are a little tricky, however it is just that a tipical FAA question and I would not worry too much about that specific question. With that being said it is still important to know how to work the
E6B and the proper sequence of steps to get the correct answer. Remember alot of the questions being asked on the exam are just for that and you will not see alot of that info again.
Good luck with your training!
CFII
 
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