How do you determine Effective Runway Le

[Richie]

§ 135.361:
(b) For the purpose of this subpart, "effective length of the runway," for landing means the distance from the point at which the obstruction clearance plane associated with the approach end of the runway intersects the centerline of the runway to the far end of the runway.
(c) For the purpose of this subpart, "obstruction clearance plane" means a plane sloping upward from the runway at a slope of 1:20 to the horizontal, and tangent to or clearing all obstructions within a specified area surrounding the runway as shown in a profile view of that area…

§ 135.385:
(b) Except as provided in paragraph (c), (d), or (e) of this section, no person operating a turbine engine powered large transport category airplane may takeoff that airplane unless its weight on arrival, allowing for normal consumption of fuel and oil in flight (in accordance with the landing distance in the Airplane Flight Manual for the elevation of the destination airport and the wind conditions anticipated there at the time of landing), would allow a full stop landing at the intended destination airport within 60 percent of the “effective length of each runway” described below from a point 50 feet above the intersection of the obstruction clearance plane and the runway.

The Question is:
If the only information available is the information given on an approach chart or the A/FD, how does a (normal) pilot determine the effective runway length at various different airports for practical day-to-day operations?

Effective runway length is absolutely essential for calculating the 60% (destination) or 70% (alternate) landing distance requirement, but there does not seem to be any way of calculating it from the information available.

Thanks

 

[tarp]

I'm a 121 driver and fortunately we have books (used to have Jepp's, now have ASAP data that does all the hard work for you for each airport you are going into).

My view (and I'm just taking a stab at this) is that the FAA wants you to have a stable approach to the runway. If you are using a runway serviced by an ILS and you use Jepps, your work is done by turning to the airport diagram and reading the Runway - Landing beyond column. There is a value for where the GS intercepts the runway and the distance remaining.

If you are not on an ILS serviced runway, one would hope that you pick one with a visual slope indicator. For these, if you look in the A/FD, you will see a GS angle and a TCH (threshold crossing height) for a stabilized approach to the runway.

A 1:20 ratio is the same thing as a 3.0 degree glide slope. So if you have a TCH of 60ft, let's say and you apply 1:20 ratio, you end up with 1200ft down the runway from the threshold at GS intercept.

I happened to use a Jepp ILS to check my work and they calculated a number of 1225ft. So if total runway from Threshold to end is 5,346ft and I take away 1225 ft for the GS intercept, I have 4,121ft remaining. Hagerstown, MD (HGR) as an example.

So now all you have to do is figure wind corrections, temperature, equipment available (e.g. anti-skid, Thrust reversers, etc.) and you're on your way.

I get the idea that you've got the runway and you're trying to figure if the plane will fit the runway. When you get the turbine, hopefully you'll get a service to run the numbers for landing and takeoff data.

Be careful of PAPI's and VASI's that are set at angles greater than 3.0 degrees - it doesn't change your distance calculation but you do have to keep in mind the technique that will clear obstacles and then flatten out in the flair.

Good luck.

For non-135 operators, you can use math to determine where the VASI will drop you off by applying the formula:

Distance to touchdown = TCH / TANGENT(GS angle)

Let's use our example. I have a 3 degree GS angle from the PAPI and a TCH of 60ft.

TCH (60) / TANGENT of 3 degrees

The tangent of 3 degrees is about .05, so:

60 / .05 = 1200

Get out your scientific calculators ;-)