Angle of Lead - Technique

[Sourpuss]

G'day!

I am currently preparing for an A320 TR. As I have no experience in large aircraft I have a few questions concerning general handling! I hope that someone has time to offer some advice!

During training in a light turboprop a rough rule for the Angle of lead was introduced which seemed to work very well.

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*AOL (90 degree intercept) = (GS/3)/Distance From Station

So for a 90 degree intercept of the LLZ at 10Nm and 210kts (No wind) and with a beacon at say 5 nm from the RWY I would start my final turn with an AOL 14 degrees to the BCN.

I was happy with with this rule and it worked well.
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I was then given a new instructor who happened also to be A320 capt. He was an extremely good instructor and offered me the following advice about AOL on a larger aircraft. I may have misunderstood him!

* 1% of the TAS is an approximtion of the Radius of Turn
Then use 1:60 rule.

eg. 1% of 210 is a radius of approx. 2 Nm. At 5 Nm from the beacon that gives an AOL of 24 degrees!
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I wrote this post fairly quickly, hopefully I didnt make any large calc. errors!

I would be greatful to hear from pilots on the 320 or 737 etc (or similar size) who may have a technique to share which serves them well. I thought that the 1st rule I learnt would also be useable on the A320 however I am now unsure because of the huge difference in AOL from one technique to the other. I think perhaps the rule for radius of turn is too rough and gives too large a value? What sort of radius would one expect in an A320 at 210kts?

Thank you in advance!

SP

[Old Smokey]

* 1% of the TAS is an approximtion of the Radius of Turn
It works well. Of course it's not perfect, but definately good enough for every day work. I taught it to students on semi-glass cockpits, and it worked well, on full FMC interceptions I find the automatic initiation of interception and my own mental calculation differ by no more than a few seconds.

Regarding the radius of turn of an A320 at 210 Kts, I don't have a calculator by my side, but I strongly suspect that it would be the same as that for a B747, A380, Lancaster, or Wright Flyer at 210 knots, provided that the bank angle was the same - sorry couldn't resist.

Regards,

Old Smokey

[Sourpuss]

hi!

Thanks for the reply. I deserved that, it was a stupidly worded question. I know that going by mv^2/r the radius should be the same but I assumed that because of the larger momentum it would take longer to enter a stabilised turn of constant radius, therefore effectively increasing the radius. A large radius is the only way I could explain why one method gives you 24 deg and one 14 deg!
Either the 1% rule or the the (gs/3)/dist is wrong but the 2nd one always worked. Which value is closer to the truth? 24 sounds a little large?

Anyway.....I guess ill wait to see what the next instructor tells me, no doubt he will have a new rule altogether!

Thanks

SP

[Old Smokey]

Sourpuss,

I have a calculator by my side now, at 210 TAS the radius of turn at 25° bank is 1.4 nm, the 1% of TAS works for 210 Kts at 17° angle of bank.

If it's good enough for PANS-OPS to use a time lag for entry / exit as you've alluded to, then I gues it's OK for we mere mortals. Allowing their 3 seconds Roll In / Roll Out, that adds a further 0.4 of a mile, making the 1.4 nm an actual of 1.8 nm, a mere 0.3 nm short of the perfect asymptotic interception. Actually, this is nice, as it gives a short "normal" intercept time at a shallow angle, or alternatively, provides some protection against an overshoot should you have a Tailwind.

Definately good enough for every-day work, please don't use it if you gain employment writing programmes for FMCs. Better then to use R=V^2/Tan Bank Angle / G.

Regards,

Old Smokey

[batty]

Dont worry too much you will get a feel for the intercepts and 95% of the places you will be flying to will be on vector anyway.

90 degree cuts are a little much on a jet and tend to establish with something like a 30 degree cut.

1% is a good ROT though, but always KISS (keep it simple stupid)

Good luck

[FlightDetent]

I was introduced to the rule as well and keep using it to much benefit. Just one side note - use the Groundspeed readout! :-)

Another neat trick is to crosscheck the "prediction" (737 gizmo, buses may have something similar) that shows 30, 60 and 90 seconds estimated track on HSI to your VSI. Makes a great companion for LP/LD continious descent approaches.

[Sourpuss]

A big thankyou to everyone who has replied to my post! It has made things much clearer.

I love this site, theres nothing you guys dont know!

Sourpuss

[Piltdown Man]

I'd use the flight director, ND and FMS. The director will generally work out the lead for you. The ND will show you the turn coming up and the FMS should show you the distance. Let the aeroplane do the work.

[DBate]

I'd use the flight director, ND and FMS. The director will generally work out the lead for you.

And what happens if you are flying a Raw Data Approach (which I prefer to a flight director approach - if weather permits)? Knowing how to calculate your angle of lead is very useful then.

So long, DBate