Turn onto x-wind and final @ 500' - why?

[Mamakim]

Just was thinking on the way back from flying lessons the other day about why we make the turn from upwind to xwind at 500' and not at say 300' or 800'?

I should of asked him there and then, but is it correct to say that the reasons are that 500' gives the standard aeroplane enough time to get the best rate of climb speed and to check that we are tracking on a straight upwind?

And what about landing......why do we turn from base to final so that on final we are at 500'........why is there this general rule and how did they arrive at the number 500'?

Might seem like a pretty silly question, but I always like to know the reasons behind the theory or in this case the numbers!


Thanks all.........


MK

[Tinstaafl]

Because Oz rules specify that the turn after take-off must not be lower than 500'. Barring something unusual it's a waste of time (& money) to wait to make the turn at a greater height. Nothing stopping from turning later if you really wanted to.

500' turning final is a different matter. The rules state that the a/c must be on final by 500 metres from the aerodrome boundary. No height is specified.

However, consider the maths. You fly a nominal circuit at 1000' & turn base at 45 deg. from the aim point. That gives you a right angle triangle with base & final the two equal sides. All other factors being equal then the 1000' to be lost would be 500' on the first leg ie base, and 500' on the other leg ie final. Ergo, final works out at ~500', give or take a little variation in technique.

[DubTrub]

Aerodrome boundary, Tins? That make it a long approach for some, especially if the runway is well inside the boundary. Are there no Pitts' flying in Oz...how do they cope?

[markflyer6580]

As discussed in some length on here somewhere,the problem with climbing to 500' then turning,climb to 1000',turn downwind etc whilst training,in a slow arse aircraft leads to huge circuits.
I still climb to 500' now before turning in case of efato(dont want any of that in a turn at 300ft!),but then do a nice long climbing turn so I still get 1000' as i reach downwind but closer in.:ok:

[djpil]

Oz rules specify that the turn after take-off must not be lower than 500' and at non-towered airports the first turn should now be within 300 ft of circuit height (with one exception). (http://www.casa.gov.au/fsa/2005/oct/33-35.pdf)
Pitts pilots here learn to sideslip down that 500 m. First time I flew a Pitts in the USA I was severely reprimanded but I learnt to love the continuous base/final turn.

[DFC]

A lot of the rules surrounding when an aircraft can turn after departure and at what height to join final approach are based on obstacle clearance.

An aircraft that departs a licensed airfield with appropriate obstcale limitation surfaces can be assured of obstacle clearance provided that it climbs straight ahead until it is above 400ft AAL. Then it can turn and provided it climbs at the minimum gradient it is again assured of clearing all obstacles by the required margin until 1500ft or enroute minima apply. When this can't be done it is notified in the relevant procedures (limitations on turn height, higher climb gradient required, specified tracks etc). At times, the initiation of the turn will be required to be not before the departure end of the runway even if the aircraft is above 400ft before that point.

For visual manoeuvring in the vicinity of the aerodrome, again obstacle clearance is an important factor.

Here are some figures for an ICAO non-instrumenty code 1 runway (basically the lowest class of runway);

The runway is surrounded by a horizontal surface radius 2000m and 45m above the runway.

The Approach area extends out to some 1600m from the strip and has a slope of 5%

The take-off area is again some 1600m long and hs a slope of 5%.

There are other surfaces that complicate the situation but those are the main surfaces relevant to what we are discussing.

Of course, flying VFR, we can see and avoid obstacles so there is no legal requirment under ICAO or UK rules that I am aware of which prevents and aircraft operating VFR from making an early turn out or from joining approach late. Local rules may say otherwise.

What I find very interesting are the instructors who demand that;

The aircraft joins final at or above 500ft AAL; and

The aircraft descends on a stable 3deg glide path; and

The aircraft remains within the ATZ; and

Circuits are rectangular!!!!!

There is a big problem with that because the ATZ will be 2nm from the centre of the longest runway at most small airfields.

To join final at 500ft AAL, the aircraft will have to be 1 2/3nm from the threshold which is close to and possibly beyond 2nm from the runway centre point.

If the 500ft point is exactly at the ATZ boundary, making the base leg at 90 deg to final track requires the aircraft to leave the ATZ at the end of downwind.

So which is the more dangerous - a circuit that leaves the ATZ with the pilot looking over their shoulder towards that magic 45 deg cut or a closer in circuit joining final at a safe, reasonable but slightly below 500ft AAL?

Regards,

DFC

[RatherBeFlying]

DFC,

The 3 degree g/s is for the big iron. Most single engine are happy at 6 degrees which gives you better clearance over the stuff that tends to poke up around smaller airfields and leaves you with more options if the engine stops.

At my own airfield, there are considerable dropoffs at both ends and I much prefer to be well above the downslope airflow.

[DFC]

I agree but there are unfortunately a few places where instructors get students to fly the 3 deg slope!

Regards,

DFC