Precautionary Landing Procedure

[avsteve1]

Hey all,

I'm having a slight difficulty when practicing Precautionary landings. I have the whole thing down but the runway length part gets to me.
I have been using 60 knots GS when timing the length of the runway (example: 30 seconds = 30 x 100 = 3000 foot runway). However, I feel
that it's a bit too slow for my liking and I find it harder to control the aircraft while trying to look outside. I would like to start using 70 knots or so
(haven't talked to my instructor yet), but what calculation would I use to determine runway length at 70 knots (60 knots is times the seconds by 100,
so I think 70 knots would be times the seconds by 120 or so)

Finally, what would be the best way to do this calculation in your head? 60 knots is easy because you just add the 2 zeros to the time in seconds, but
I'm not the best in the world at mental math and I'm looking for ways to do it in my head faster (for example, if 70 knots is times the seconds by 120,
30 seconds x 120 = 3600 foot runway) ?

Thanks.

[lownslow]

Maybe the simplest would be to pick a speed you're comfortable with and a minimum runway length you would use, do the math on that and use this singular timing to make a go/no-go decision.

[photofly]

Fly at 70,and calculate at 60. Figure in a few knots of headwind, and you’re about correct. You’re determining if the field is suitable for landing, not surveying a land claim, so no need for pinpoint accuracy.

[Big Pistons Forever]

Fly at 70,and calculate at 60. Figure in a few knots of headwind, and you’re about correct. You’re determining if the field is suitable for landing, not surveying a land claim, so no need for pinpoint accuracy.

/\ What he said

[AirFrame]

At 180kts it's only 10 seconds for 3000 ft...

Another method is to decide what your minimum landing length is, and work out (once) how many seconds it takes to fly that length at a speed you're comfortable with. Then you only have to count off the seconds to your limit. If the runway ends before you finish counting, it's too short, go elsewhere. If it's longer, you know you have margin.

[20DMEYYZ]

what's the best endurance speed for your aircraft?

[MrTurbine]

How about more flap setting for your low and over? Slower stall speeds should keep you a little bit happier

[AirDoan]

I just had a similar thought exercise while in the shower this morning. But for me it's because I am currently pipelining but want to fly floats next year. So I often look at the lakes we fly over and want to estimate their lengths at various speeds with a rule-of-thumb guide.

If at 60Kts 1 Sec = 100' then it stands to reason that 120kts would = 200'/second. You can pretty easily extrapolate in between in 10Kt increments, and what I would do is round down to 15 from 16.6 for easy math and a tiny fudge factor. That means 15'/second every 10kts. So at 70 you would have 1 sec = 115'. Since in my low level job is usually flown between 100 - 120Kts I can make a reasonable estimate of how long a lake or field is with this.

If there is a reason this won't work, I'll differ to the more experience guys. But I doubt I am the first to think of it. LOL

[AirFrame]

If there is a reason this won't work, I'll differ to the more experience guys. But I doubt I am the first to think of it. LOL

It works, but it requires thinking more about the math. Using the round numbers (60kts=100'/s, 120kts=200'/s, 180kts=300'/s), you reduce the math into simple multiplication of simpler numbers and then adding two zeroes. Depending how urgent it is that you find a place for a precautionary landing, your brain may appreciate having a few more cycles available.