Cat C Circling Manoeuvre

[quarefellah]

Hi All,
Flying a Cat C type aircraft and was wondering is there a standard circling manoeuvre or does each manufacturer have their own version of perfection? I'm referring specifically to circling to the opposite end of the IAP runway. I know the break off is 45 degrees but for how long and is that adjusted for wind? If so what's the wind correction for that leg? Likewise, on the downwind, when timing from abeam the threshold how far do you go in terms of time and how is that corrected for wind?
Just canvassing for views and checking we're doing it right.

Safe Flying
QF

[Wingswinger]

Flying a Cat C type aircraft and was wondering is there a standard circling manoeuvre or does each manufacturer have their own version of perfection?

Don't know

I'm referring specifically to circling to the opposite end of the IAP runway. I know the break off is 45 degrees but for how long and is that adjusted for wind?

45 deg off for 30 " from wings level unadjusted for wind.

Likewise, on the downwind, when timing from abeam the threshold how far do you go in terms of time and how is that corrected for wind?

It depends on circling height above touch down elevation - 20" for the first 500ft and add 2" per 100ft above 500ft corrected by 1" per 2kts head/tail wind (usually tail).

That's for A320 series.

HTH,

WS

[zonnair]

This are all guidelines. (to be followed as muchs as possible). At the end you can do it the way you want, as long as you remain visual contact with the runway at all times and within the circling manoeuvring area = 4,2 NM (pan-ops)

[BOAC]

Since we know nothing about 'quarefellah' it is worth cautioning him/?her? that Terps allow only 1.7nm from the end of all runways for their minima as opposed to 4.2nm for PansOps.

Cicling can be determined
a) on prescribed tracks
b) without prescribed tracks
-refer to individual airfields to find out.

In broad brush terms:
If a) you are expected to follow the tracks
If b) then as long as you stick to the sighting rules, prescribed area and minimum heights you can fly how you like around the field.

[zonnair]

Thanks for the addition.

[gatbusdriver]

I believe TERPS uses 25 degrees AOB whilst PAN-OPS uses 20.

For 757 (for us)

Establish on IAP Gr Dn flap 20 (if ILS remember not to arm App). On reaching circling alt in alt hold set MAP alt. When visual break off 45 degrees for 45 secs (can do 80/80). Downwind, abeam the threshold fly for 3secs/100' (we use +/- 1sec/1kt H/T). Start base with gradual descent (3-400'/min). Flap 30.

MAP to be flown is the one associated with the initial IAP flown.

[Checkboard]

Flying a Cat C type aircraft and was wondering is there a standard circling manoeuvre or does each manufacturer have their own version of perfection?

No, each company uses the manufacturer's advice in the manufacturer's training document, then changes it according to the experience (or lack of) of the training department.

I'm referring specifically to circling to the opposite end of the IAP runway. I know the break off is 45 degrees but for how long and is that adjusted for wind?

45 deg off for 45 seconds from wings level ± 1 second/2 knots wind. Previous company never had a time guidance, as most circling was from an off-axis non-precision final approach. Generic advice was to position onto a 1.7 mile abeam downwind (this was ¾ of the first range ring on the lowest scale EFIS map on the 737-300, which is the second lowest scale on the NG) One times drift heading into wind (drift away from runway), three times drift into wind if drift is towards the runway.

Likewise, on the downwind, when timing from abeam the threshold how far do you go in terms of time and how is that corrected for wind?

45 seconds ± 1 second/2knots wind. Previous company was 30 seconds or three times the height AGL in seconds (whichever larger) no wind correction. On the 737 EFIS map, the base of the aircraft triangle ahould be abeam the threshold (useful to know if you forgot to start the clock!)

Cicling can be determined
a) on prescribed tracks
b) without prescribed tracks
-refer to individual airfields to find out.

Some airfields with circling on prescribed tracks may also allow "normal" circling inside the circling area, if requested. In France, for instance, this is referred to as MVL or MVI (?) circling. If you don't want to use the prescribed track (e.g. to avoid weather) then you request MVL circling from ATC.

[Tee Emm]

Start base with gradual descent (3-400'/min). Flap 30.

Not necessarily so - especially at night where ground features may not be discernible and it is impossible to see if you are maintaining safe terrain clearance of 400 ft (Cat C). Once you deliberately elect to descend below the published circling MDA on downwind or base, you are entirely responsible for your own terrain clearance. Only a courageous pilot would risk descending on base until you are established within the approach splay. In some countries a PAPI or VASIS may be seen on base leg but obstacle clearance not guaranteed until within plus or minus 15 degrees either side of extended runway centre-line. Short answer: Don't descend until on final.

With regard to timing of the downwind leg. The timing policy was an old one from countless years back when bad weather low level circuits sometime encountered IMC during parts of the downwind leg. In those cases timing was the method used depending on height and it was acceptable to go IMC but for short periods only. Hence timing. In those days a circling MDA hadn't been invented and it was a case of preflight study of relevant aerodrome charts and familiarity with the terrain.

With the advent of DME or availibility of a reliable distance aid, there is nothing to stop you from extending downwind to keep within the limits of 4.2 nm circling MDA (ICAO). After all that is why the distance limit is published as part of aircraft categories. It is another story altogether if you are unable to keep the aerodrome in sight because of reduced visibility. A missed approach would have to be conducted. But if visibility is not restricted, then use the extra distance downwind to avoid the problem of being too high on base and final for a stabilised approach.

With a relatively high circling MDA there is a myth that at night you can descend below the circling MDA (potentially dangerous unless you know exactly the position of the critical obstacle that dictates the MDA) at any time downwind or base in order to suit the profile of your aircraft type. The designers of the published circling MDA couldn't care less about your profile descent problem. It then becomes your problem and the vultures await your custom if you choose to drop below the published MDA at night until safely ensconced on final.

[RYR738_driver]

Another question with regard to circling manoevre and protected areas.

Pans Ops says you must stay within 4.2nm of the thresholds of all runways. Does that mean that the controlling authority must ensure this area is kept clear from other aircraft?

For example, Pisa, VOR DME Approach 04 Left, circle to land R22 Right, upon breaking right for a left hand downwind, tower cleared a company aircraft to take off on R22 Right. I've no problem with this as we were downwind at this point and obviously fully visual with airfield and terrain.

My only problem would be if, as we broke right decided to go around, and the go around procedure (for argument sakes) was straight ahead on 04 Left, then we could potentially be in conflict with the a/c taking off

Is the controller correct to allow the aircraft to take off?

[BOAC]

I cannot see what the prolem is - the controller waited until you were on a divergent track, yes? If you then 'decided' to carry out a g/a, you would turn the shortest way back onto the centreline of 04L to fly the g/a, by which time you would have been well clear of the outbound track, and, of course, carrying out a visual manoeuvre, the controller would no doubt expect you not to hit the departing.

[Checkboard]

Hmmm Pretty poor post, Tee Emm!

Not necessarily so - especially at night where ground features may not be discernible and it is impossible to see if you are maintaining safe terrain clearance of 400 ft (Cat C).

The 400' terrain clearance for visual manoeuvring in Australia is for daytime only, as I recall.

Once you deliberately elect to descend below the published circling MDA on downwind or base, you are entirely responsible for your own terrain clearance. Only a courageous pilot would risk descending on base until you are established within the approach splay.

Not so, the whole point of visual circling, is that you are maintaining visual terrain clearance. With that terrain clearance (i.e. seeing the ground - you may descend safely. Every flight has to get pretty close to the ground to land!

In some countries a PAPI or VASIS may be seen on base leg but obstacle clearance not guaranteed until within plus or minus 15 degrees either side of extended runway centre-line. Short answer: Don't descend until on final.

See above. That statement is simply not correct.

With regard to timing of the downwind leg. The timing policy was an old one from countless years back when bad weather low level circuits sometime encountered IMC during parts of the downwind leg.

Timing a circuit is not usually policy - it is a technique. "Countless years back" must mean 1920 or so!! ANY aircraft circling who encounters IMC (even in 1920) is no longer visual circling!

In those cases timing was the method used depending on height and it was acceptable to go IMC but for short periods only.

See above - silly comment.

Hence timing. In those days a circling MDA hadn't been invented and it was a case of preflight study of relevant aerodrome charts and familiarity with the terrain.

Yes - in 1920, or before - is this a history lesson?

With the advent of DME or availibility of a reliable distance aid, there is nothing to stop you from extending downwind to keep within the limits of 4.2 nm circling MDA (ICAO).

Whilst a quick look at some guidance is OK, you appear to be assuming every DME is located at the landing runway threshold here!

With a relatively high circling MDA there is a myth that at night you can descend below the circling MDA (potentially dangerous unless you know exactly the position of the critical obstacle that dictates the MDA) at any time downwind or base in order to suit the profile of your aircraft type.

It is not "a myth" - it is approved procedure! You descend according to your descent profile. As you have the runway, or lights associated with the runway in sight, you have a straight line of sight, which = no terrain in between for a standard descent.

The designers of the published circling MDA couldn't care less about your profile descent problem.

No, they don't. That's because the circling MDA is for circling - the descent to the runway is not circling.

[capt. solipsist]

Checkboard,

You beat me to the punch.

Cheers!!!

[Tee Emm]

The 400' terrain clearance for visual manoeuvring in Australia is for daytime only, as I recall.

Thanks for that info. I was unaware that the Cat C circling of 400 feet above terrain/obstacle did not apply at night. In that case what is the mandatory terrain clearance (if any) at night during circling? The sarcastic reference to the 1920's in your other replies indicates a degree of immaturity. Kindly refrain.

[A37575]

Quote:
In some countries a PAPI or VASIS may be seen on base leg but obstacle clearance not guaranteed until within plus or minus 15 degrees either side of extended runway centre-line. Short answer: Don't descend until on final.
See above. That statement is simply not correct.

From AIP Australia:

Note 1. T-VASIS. The night azimuth splay is normally increased to 30 degrees to permit T-VASIS to be visible on base leg. However, obstacle clearance is not guaranteed until the aircraft is within the approach obstacle clearance surface. Accordingly, T-VASIS should not be used for approach slope guidance until the aircraft is aligned with the runway.

[aterpster]

Since we know nothing about 'quarefellah' it is worth cautioning him/?her? that Terps allow only 1.7nm from the end of all runways for their minima as opposed to 4.2nm for PansOps.

China Airlines learned that the hard way in Korea a few years ago.

The TERPs circling criteria are absurd and have been held in disdain by all safety experts for years. Arguments have been made before the FAA for improved criteria.

Finally, the FAA did approve greatly improved circling criteria in Change 21 to TERPs but unending FAA politics are keeping those changes from being published.

[A37575]

As you have the runway, or lights associated with the runway in sight, you have a straight line of sight, which = no terrain in between for a standard descent.

Circa 1960 a PANAM 707 flew into a mountain at night on descent into Bali. The crew reported airport lights in sight on descent. However, the airport lights suddenly disappeared from view due to terrain between aircraft and airport. The crew of the 707 thought it was a momentary cloud and continued descent. They were wrong.

[Checkboard]

After the Monarch Piper Chieftain disaster, in which the aircraft flew into the ground while circling at night, the Australian AIP was changed so that descending to a 400' visual terrain clearance at night was prohibited - all circling at night must be at the circling MDA, until a constant descent to the runway is commenced.

I've been away from Oz for a while, so don't have the reference.

1920 refers to the Air Navigation Act of 1920.

When I said "That statement is simply not correct." I was referring to the "Don't descend until on final." statement. Not very clear, I know.