CAT III Field length factor

[mischo1990]

Hey guys. Just wanted to ask a quick question about the field length factor in the CAT III apps. I need an quick explanation of this: ....For operations with a controlling runway visual range (RVR) at or above 600 feet the required field length is 1.15 times the field length. What does that mean to a pilot?

[eckhard]

Not familiar with your quoted extract from the regs but in general, an auto land uses a bit more runway than a manual landing. Your AFM, FCOM or Ops Manual will give type-specific additions to LDR.

[mischo1990]

Sorry for the post but after 3 hours of browsing and searching the FAA pages i found the answer for my question:

(1) The destination runway length shall be determined prior to takeoff to be at least
115 percent of the runway field length required by the provisions of 14 CFR part 121,
§ 121.195(b).
The calculation shall be made prior takeoff with the actual GrossW and there should be a 15% margin in the calculated length and the available length

[MarkerInbound]

To dispatch a jet airliner under the FAA FARs it must be planned to arrival at the destination at a weight that will allow it to come to a full stop within 60% of the available runway. If the runway is wet, the available stopping distance must be 115% of the dry stopping distance. The rule is written to allow the use of dry stopping distance charts on a wet runway. Since most airports don't stretch their runways when they're wet, the easy way to think of this is the dry stopping distance must be ~52% of the available stopping distance if the runway is wet. Most operators consider the runway wet when the visibility is reduced below a certain value.

[mischo1990]

So let me make it straight on a simple example. 1000m long runway at the destination airport. Actual weight weight over DEST airport calculates i will stop on 600m of the DRY rwy. If the RWY is WET we assume 600m+15% = 690m.
So the OPT has to give me values 600m DRY or 690m WET to be LEGAL do dispatch. :hmm:

[MarkerInbound]

No. You would have to find a runway 1150m at that weight. Given that fresh concrete won't cure while you are enroute you have to work with what you have. You have to work backwards from your 1000m. If your weight allows a landing distance of 869m dry you would be good for a 1000m wet runway. (869x1.15=999.35).

[mischo1990]

Perfect, thank for the explanation Marker :) :)