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Welcome to the CPL Navigation question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.

lucasgozzard created the topic: Answer discrepancy Simple 1 in 60 from the WAC

Hi Bob,

Just completed Question 1 from the Simple 1 in 60 exercises from the WAC on page 113.

My answers seem to be a little different from yours and am worried what tolerances they allow in the exam.

My answers to Scenario 1 are as follows:

FPT = 025 degrees M
TE = 12 degrees
TMG = 013 degrees M
CA = 5 degrees
TTI = 030 degrees M
HDG change req = 17 degrees R
HDG to fly after off track fix = 045 degrees M
GS = 133 kts
ETA at destination = 0304
Drift = 15 degrees L
HDG that would have kept the aircraft on track = 040 degrees M

bobtait replied the topic: Answer discrepancy Simple 1 in 60 from the WAC

There is nothing wrong with your reasoning. Sometimes, a measured distance may not be a whole number and that could give you a slightly different answer, especially when dealing with TE or CA. Remember that the one-in-sixty rule is not mathematically precise in any case. It's a 'rule of thumb'. It doesn't make much sense to argue about a fraction of a mile or a fraction of a degree. How perfectly can you hold a heading in practice?

John.Heddles replied the topic: Answer discrepancy Simple 1 in 60 from the WAC

Some follow up on Bob's comments.

The 1:60 "rule" is an approximation based on some basic relationships for angles measured in radians. For smallish angles (say, less than 12-15 degrees) it is quite accurate to use the angle measure as being equal to trigonometric ratios of interest. So, really, it should be the 1:57.3 (approximately, as pi comes into the reckoning) rule. Being interested in looking for simple ways of doing stuff, 57.3 is pretty close to 60, so we end up with the 1:60 rule.

A bit of sideline, useless information to tuck away, I guess.

Engineering specialist in aircraft performance and weight control.