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4 Rules-Of-Thumb For End-Of-Summer Flying

1) Takeoff roll increases about 10% for every additional 1,000 feet of density altitude

There's still no shortage of hot-weather days left this summer. And on hot days, you get high density altitude.

For most normally-aspirated GA airplanes, you'll add about 10% of takeoff roll for every 1,000' of DA.

For example, if your airport's density altitude on a hot day is 3,200' over field elevation, you'll increase your takeoff roll by about 32% over an ISA day.

So if you have a 1,500' takeoff roll on an ISA day, you'll increase that roll to almost 2,000'.


2) Stay a minimum of 5 miles from storms, and up to 20 miles if you can.

Flying closer than 5 miles from visible overhanging areas in storm clouds puts you at risk of flying through hail and severe turbulence. That's not good for your plane, or your passengers.

In some cases, aircraft have encountered hail, severe windshear, and severe turbulence up to 20 miles from storms.

When in doubt, keep your distance.

GolfCharlie232

3) Calculating Civil Twilight

A good rule-of-thumb for calculating civil twilight is that it usually ends between 20-35 minutes after sunset. Tonight in Boulder, CO, sunset is at 8:02 PM, and civil twilight ends at 8:31 PM. That's a difference of 29 minutes.

Once twilight ends, you can start logging night flight time. But remember, you need to wait an hour after sunset to log night landings.


4) Add Half The Gust Factor On Windy Day Landings

As we approach the end of summer, windy days increase across the US, because the jet stream starts moving south.

When you're dealing with a gusty day, the FAA recommends that you add half the gust factor to your final approach speed to give yourself safe padding from a stall.

For example, if the winds are reported at 18 knots, gusting to 30 knots, it means you have a gust factor of 12 knots (30-18 = 12). So if you take half the gust factor, you get 6 knots (12/2 = 6).

Boldmethod

To apply that in an SR-22T, Cirrus recommends that you fly final at 80 knots. So on a day with a 12 knot gust factor, you'd add 6 knots to the published 80 knots, for a final approach speed of 86 knots.

The same math works for any GA airplane's final approach speed. Just add half the gust factor to your final approach speed.

Boldmethod

What other rules-of-thumb are helping you out this summer? Tell us in the comments.

Colin Cutler

Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed development of numerous commercial and military training systems. You can reach him at colin@boldmethod.com.

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