About the Calculation (AKA "Alternate Step 5"):
See figure 2.5.3 (p2-44) in the FOM.

You might be able to use this procedure if:

• If your achievable 2nd segment climb gradient (from the AFM) is close to, but not quite good enough for the required or published climb gradient, AND
• you've got a relatively long runway available, AND
• the published top of the climb on the departure is relatively low...

The object of the calculation is simply to determine the maximum takeoff distance which would allow you to make the published climb gradient, by taking credit for unused runway. This tool does the calculation for you (including rounding the "runway length decrement" up to the nearest 1000ft, as per the FOM), and displays the result on the last line.  You need only enter the following 5 numbers:

• Obstacle Clearance Altitude - top of the climb, MSL, from the published departure procedure.
• Departure End of Runway (DER) elevation, MSL.
• Published Climb Gradient - "what you must do", from departure procedure, in ft/nm.
• Desired Climb Gradient - "what you can do", from the AFM, in % gradient.
• Runway Length Available - total distance available for takeoff.
• Note: Gray fields are calculated by the tool and do not accept user input. These include the 2 climb gradient numbers, which are displayed in both ft/nm and % grade for comparison purposes.

Result ("T/O Dist Limit") - Compare the result to your required takeoff distance (from the AFM, dispatch flight release, or other source of certified performance data).

• Required takeoff distance must be less than the calculated T/O Dist Limit, or it's a no-go.
• If the T/O Dist Limit is negative, it means that with the specified circumstances your takeoff would have to be complete (i.e. start of 1st segment climb) prior to the start of the runway. Physically impossible (obviously), so this result is shown in red.

"Real World" uses:
KLGA: LaGuardia 1 departure (excluding the Coney & Maspeth climbs - probably)
KSFO: All departures including Dumbarton 6, Eugen 5, Gap 3, Luvve 2, Molen 3, Offshore 5, Porte 3, Quiet 2, Rebas 3, San Francisco 8 & Shoreline 1
If you come across any others, send them to me and I'll post them: karl@kwvv.net

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