Circuit timing abeam threshold.

[Pin Head]

Hi

Normally use 3 X your height in hundreds of feet +- twc/hwc

Some people use full wind from prog 2 while others use 1/2.

Which is best and why?

Thank you.

Pin

[de facto]

i use 2 secs for each 10 kts of wind.
I also calculate based on my expected ground speed,the distance from threshold at which i will turn.
A distance wich should allow you to still see the runway based on given/required visibility.
For example a visual at 1500 agl,at flaps 5/speed 170 and tw 10kts equals to 180 kts GS.
180 kts is 3 nm/min...basic visual is a turn started at 2NM,so my timing should coincide with 43sec.....more or less 3Xheight.

[Piltdown Man]

For 1,500'? - Start your stopwatch abeam the threshold downwind. When the stopwatch hits 30 seconds or when it looks right, start your turn and land. Precision to the second is what the Skygods use. The rest of us us TLAR.

PM

ps. TLAR = That Looks About Right

[de facto]

For 1500,airbus calls for 45 sec,,,basic 3*100.same as used for circling.
Sky gods are also aware of visual illusions,downslope/upslope terrain,poor lighting...and stabilised criteria based on rate of descent.
But go ahead turn after 30 sec,be my guest,make sure you always turn base in the direction you are seated as well...its easier to see as well:ok:

[Johnny F@rt Pants]

3 X your height above airfield as others have said works very well. Then use 1/2 your height for your V/S to set once you turn base, brings you close enough to 3°, of course this is all different if the glide path angle is different.

With regards to wind, there are several methods, the most common that I have come across are -

1 - don't change the timing, what you gain in one direction you lose when you go the other.

2 - add/subtract 1 second per knot of head/tailwind.

3 - (the one I use and teach)add/subtract 1 second per 2 knots of head/tailwind.

[de facto]

1/no info by boeing
2/used by airbus
3/good enough
Few variables,main is to have an idea of your total track miles(base+final) to plan your rate of descent.
A visual normally gets you 5 miles,a circling is dependent on your height and the limit imposed by the actual visibility.
A 5000 m max visibility (2.7 nm) for a circling will mean that you will have to turn base around 2.2 nm,otherwise you will lose sight of the runway....depending on that factor and your circling height,timing may not be sufficient/acceptable to start the turn and you may have to increase your landing flaps to help with descent planning(lower speed/same rate..more time to lose altitude...)

[B737900er]

Where in the Boeing manuals does it mention about timings?

[de facto]

It does not,but if you are expecting Boeing to prechew every single aspect of flying,you are mistaken,it is not their philosophy.
However,Airbus does...you can learn a lot more by reading their manuals.
By the way,3 secs/100 feet,so 45 secs on visual circuit at flaps 5 speed will get you exactly if not quite close to the 2 nm base turn depicted in boeing visual maneuver.

[B737900er]

Thanks De facto.

[shlittlenellie]

Most circuits joined commercially won't be at 1500' AGL and will be descending joins. Dragging around the circuit at 1500' would be unusual, other than after a go-around.

For a 737 with config gear and flap 15, 757/767: gear and flap 20, Airbus gear and flap 2? (never flown, sadly):
1.5 x height in hundreds of feet = seconds in still air from the threshold before turning base-final, e.g. 4000' = 60s.

+/- half the wind (usually a tailwind on the downwind, but not always!)

The above timing works for 3000' and above. Eyes out of the window is crucial since the wind/temperature/up/down drafts will skew the numbers slightly and it is a visual manoeuvre.

Remember also the circling area at night (and it's not madness to consider it during the day with a view to operating in at night). In a descending circuit, 4200' and 5200' abeam the threshold, respectively, will remain just within cat C and D circiling areas (ICAO): provided the configuration above is used - otherwise the aircraft will sail outside of the circiling area, "I'll just extend a bit", "Noooooo".

[Pin Head]

Yes. All good.

Why can cat c use cat d for defined area?

[ooizcalling]

Trouble with the 3 times method is that it may take you outside the protected circling area for your category. So you really need to consider the next higher category circling minima. If its nice VFR weather, no problems (log it as x-country time;-)