CRFI and Factors

[xlwing]

So this is confusing and very unclear.
Say you are 704 operating a turbo-prop with reverse/disc. You calculate your AFM landing distance to be 2800' and the runway you're intending to use is 5000' long. The CRFI is 0.60 and no wind.

Are you limited for takeoff??

From my understanding, 70% of 5000 is 3500 so that is your limit to which you must come to a full stop taking into account wind and CRFI. Looking at 0.60 for 2800' gives 4460'. This value is beyond the 3500 (70%), thus are unable to depart legally?

[Vanguard]

I don't know but it seems like you're missing some details here.

There's no wind ...CRFI is 0.6 ... 5000ft.. In real life situation.. You'd be on the ground safely. What kind of aircraft are we talking about? A B1900 would have no problem in the conditions you've outlined.

Where are you getting that 70% value from?

[AOW]

704.49 (1) Subject to subsection (3), no person shall dispatch or conduct a take-off in a turbo-jet-powered aeroplane or in a large aeroplane unless
(a) the weight of the aeroplane on landing at the destination aerodrome will allow a full-stop landing
(i) in the case of a turbo-jet-powered aeroplane, within 60 per cent of the landing distance available (LDA), or
(ii) in the case of a propeller-driven aeroplane, within 70 per cent of the landing distance available (LDA); and
(b) the weight of the aeroplane on landing at the alternate aerodrome will allow a full-stop landing
(i) in the case of a turbo-jet-powered aeroplane, within 60 per cent of the landing distance available (LDA), or
(ii) in the case of a propeller-driven aeroplane, within 70 per cent of the landing distance available (LDA).
(2) In determining whether an aeroplane can be dispatched or a take-off can be conducted in accordance with subsection (1), the following shall be taken into account:
(a) the pressure-altitude at the destination aerodrome and at the alternate aerodrome;
(b) not more than 50 per cent of the reported headwind component or not less than 150 per cent of the reported tailwind component; and
(c) that the aeroplane must be landed on a suitable runway, considering the wind speed and direction, the ground handling characteristics of the aeroplane, and other conditions such as landing aids and terrain.
(3) Where conditions at the destination aerodrome at the time of take-off do not permit compliance with paragraph (2)(c), an aeroplane may be dispatched and a take-off conducted if the alternate aerodrome designated in the operational flight plan permits, at the time of take-off, compliance with paragraph (1)(b) and subsection (2).

Nowhere in there does it talk about CRFI. The 70% factor is a dispatch limitation, while CRFI is an operational limitation. There is no forecast CRFI, so you can't predict what it will be at time of landing, so dispatch doesn't have to account for that; good airmanship would encourage you to make an educated guess (last CRFI was 0.05, and nobody is working on it, so it probably isn't going to get better by the time I get there!).

The CRFI recommended landing distance tables let you enter based on CRFI and either Landing Distance or Landing Field Length (either 60% factor or 70% factor). So if your flight manual is based on an already factored landing field length, look that up at the right side, and find the column for the CRFI and you have your recommended field length. If your flight manual gives you an unfactored landing distance, enter from the left side, and find the CRFI column.

CRFI2.jpg (271.6 KiB) Viewed 3874 times

So if your example was a 2800 foot landing distance, at .60 CRFI, the recommended field length is 4460. But if 2800 feet is the 70% factored landing field length, then the recommended field length is about 3340.

tl;dr you don't double factor!

[xlwing]

Yes - a B1900 for example. Its AFM calculates based on non-factored values. I realize it can easily do it, but the concern would be the legalities.

Wouldn't "the ground handling characteristics" in 704.49 (2)(c) pertain to taking into account the expected CRFI in the calculation with regards to dispatch? A lot of companies also restrict dispatch based on latest CRFI report.

And a 2800' (unfactored) landing distance gives a 4460' landing distance or "recommended field length"? It says recommended landing distance as the title of the RFI columns.

[AOW]

Wouldn't "the ground handling characteristics" in 704.49 (2)(c) pertain to taking into account the expected CRFI in the calculation with regards to dispatch?

I understood that to refer to crosswind limitations, which you could argue vary depending on CRFI, so it does come into play, but is more to do with the suitability of the runway than the landing distance.

A lot of companies also restrict dispatch based on latest CRFI report.

That makes the most sense, as long as LDA >= recommended landing distance based on CRFI >= factored landing field length.

And a 2800' (unfactored) landing distance gives a 4460' landing distance or "recommended field length"? It says recommended landing distance as the title of the RFI columns.

Yes, you are correct that it is a recommended landing distance, as in make sure that LDA is at least this much. It does not mean make sure that LDA is 1.43 * this, as that would be double factoring. You could even go as far as arguing that since it is "recommended" it is not limiting, however good luck with that defense should you go off the end! Realistically, one should be able to get a 1900 stopped in 4460', even if the runway is 100% polished ice, with a generous coating of oil to ensure that you have no chance of getting any grip, but be warned that directional control may not be a thing in that case!