Flying Wisdom

Flying Wisdom that should prove useful to you

The Rule of 4 (or 3, or 5, or ...)

This rule of thumb is used to decide when/where to start your descent. (The Rule of 4 is used for aircraft with a roughly 120 KTS ground speed during descent. Use 3 = 90 KTS, 4 = 120 KTS, 5 = 150 KTS, 6 = 180 KTS, etc.)

Subtract your target altitude from your cruise altitude and then convert to 1000s of feet and multiply that number by 4. This gives you the number of nautical miles out that you should start a 500 feet per minute descent.

Example: 7500 cruise, 1000 pattern altitude. ((7500 - 1000) / 1000) * 4 = 26. This means to start your 500 FPM descent 26 NM before your target.

Rule of 300 (for a 3° descent)

The rule of 4 is great (see above), and is my go-to rule descent planning for VFR flight. But sometimes -- such as when flying IFR in higher performance aircraft -- you may prefer to descend on a 3° descent path rather than 500 FPM.

The rule of 300 starts out the same as the rule of 4. But instead of dividing by 1000 and then multiplying by 4 you divide by 300.

Example: 7500 cruise, 1000 pattern altitude. ((7500 - 1000) / 300 = 20. This means to start your 3° descent 20 NM before your target.

Never exceed 30° of bank in the pattern

This rule of thumb is intended to keep you safe and to help you avoid a stall/spin accident near the ground. By limiting your pattern bank angle to 30° you minimize the associated loss of lift and minimize the increase in stall speed.

Bank angles of 20°-25° are typically all you need to fly a proper pattern.

70% of takeoff speed by midpoint of runway

You should reach 70 percent of your lift-off airspeed (or greater) by the midpoint of the runway. If you do not reach this speed by this point then you should abort the takeoff. (See AIM 7-5-7.)

Estimating Crosswinds

Don't have your crosswind chart or E6B handy? Here is a good way to estimate your crosswind component: Calculate the angle between your runway and the current winds. For example, if you are using runway 31 and the reported winds are 340 @ 10 kts, the crosswind angle is 30°.

Now use the following value pairs to estimate the percentage of the winds that comprise the crosswind component: 0° => 0%, 15° => 25%, 30° => 50%, 45° => 75%, 60° or greater => 100%. So in our example, the crosswind component would be 50% or 5 kts. You can do linear interpolation between values if you want, but it is largely unnecessary.

Rate of Descent for a 3° glideslope / descent path

To calculate your required rate of descent in feet per minute, divide your ground speed by 2 and add a zero to the end. For example, if you are on approach at 60 kts ground speed then you need to descend at 300 FPM.

Density Altitude

Rule of thumb: For every 1°C above ISA standard temperature (for the given altitude), the density altitude (DA) increases 120 feet. For example, if the temperature is 25°C at 5000 feet, it's 20°C over ISA. 20 * 120 = 2400 feet higher, or a DA of 7400 feet.

Impact of Density Altitude on Takeoff Performance

For each 1°C above ISA standard temperature the takeoff role increases by 1%. For example, if the temperature is 10°C above standard the takeoff roll would increase by approximately 10%.

Bank angle for standard rate turn

10% of your TAS (in knots) + 5

For example, if your TAS is 120 kts use 12 + 5 = 17° of bank.

When to start your roll out from a turn

Start your roll out at half the bank angle.

For example, if you are banked at 20°, start your rollout at 10° before your target heading.

When leveling out after a climb ...

... leave your power at climb power until your airspeed reaches your expected cruise speed. Then reduce your power to the appropriate cruise power setting and lean if/as appropriate. This will help you reach your cruise speed sooner and therefore minimize the time it will take to get the aircraft properly trimmed and fully set for cruise.

When leveling out after a descent ...

... use the same basic idea as for climb, but adjusted for descent: Add power back in as the aircraft levels off so as to obtain and maintain your intended cruise speed as efficiently as possible. Trim and lean as appropriate for cruise.

Take-off Pitch

Typical takeoff pitch is about 10° nose up. Make minor adjustments if/as needed to maintain Vx, Vy, or other speed as appropriate for your initial climb out.

En-route Climb Pitch

Typical en-route climb pitch is about 5°-7.5°, depending on exactly what climb rate or climb airspeed that you are trying to achieve.

Level Flight Pitch

At normal cruise speeds most aircraft will show about 0° of pitch (this is by design and relates to the angle of incidence). As you slow down you will need to increase your pitch to maintain level flight.

Descent Pitch

A nose down pitch of 2.5° will result in a 500 FPM descent rate at a ground speed of 120 kts.

Descent Gradient

For every 1° of descent angle you will descend 100 feet per NM. For example, a 3° descent angle (a typical glide slope) will result in a descent gradient of 300 feet per NM.

Here's another way to use this: If you have 10 NM to descend 5000 feet you would need a 5° descent angle (nose down pitch).

Don't chase your airspeed

When climbing or descending many pilots (student pilots and licensed pilots alike) tend to overshoot and undershoot their target airspeed and may, or may not, eventually settle at the target airspeed. The main cause of this is "chasing the airspeed" - pushing the nose down or pulling the nose up until the reaching their target airspeed without paying attention to the current trend (climb/descent rate). This results in oscillations of pitch and airspeed.

When you hit your target airspeed your change in climb/descent rate should be zero. To achieve this, control your pitch and make deliberate but minor changes to reach your intended airspeed with (near) zero change in climb/descent rate. Try not to overshoot.

How to convert Jet-A pounds to gallons

Turbine aircraft typically give burn rate in pounds per hour (PPH) and fuel remaining in pounds. Yet when you need to take on fuel the FBO wants your order in gallons. To convert from pounds to gallons divide by ten, add half, and then change the units from pounds to gallons.

Example: 800 pounds: 80 + 40 = 120 gallons