Plane & Pilot
Tuesday, February 21, 2012

Murphy’s Laws Of Aviation

Why what you learned in flight school may be open to question

I'm constantly amazed that the constants of aviation usually aren't. Many friends, retired airline and military pilots, tell me their experience reflects the same truths. It seems there are a number of popular myths about flying that refuse to die.

One of the most common is that experience is the best teacher. The myth is that aviation is such an unforgiving discipline that you may never live to make the same mistakes twice. While that's true for several of the cardinal sins, it's apparently not applicable for most minor infractions.

I'm living proof. I've made many of the same mistakes two or 10 times, and still somehow managed to walk away. Perhaps best of all, no one else knows about my transgressions.

One thing I've learned, however, is that many of the rules of thumb (and forefinger) we were taught in flight school are simply not true. Or at least, not all the time.

One of the most common misconceptions is that tailwinds should logically cancel comparable headwinds as long as you make round-trip flights and wind direction doesn't change.

Sorry, it doesn't work that way. I'm not sure what the real statistics are, but I'd bet you'll experience headwinds at least 70% of the time. First, a given headwind is more of a disadvantage than an equivalent tailwind is an advantage, because a headwind acts on the airplane longer than a tailwind. Second, even a direct crosswind costs you speed because the aircraft is crabbing partially sideways. Do the math, and you'll find you gain speed from a tailwind in only about the aft 160 degrees, but lose speed from any wind in the forward 200 degrees, obviously not a fair trade.

For flight planning purposes, many of us ignore tailwinds of less than 10 knots and assume we'll break even if we're lucky. The cynics among us also add 20% to any headwind.

We were all taught in flight school that fuel reserves need to be enough for the planned flight plus a 30-minute reserve on VFR day legs, planned flight plus alternate plus 45 minutes for IFR hops.


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