Circling below circling MDA at night.

[HSWL]

Circling approach at night where you can see the runway lights no problem, but due darkness you cannot see the ground ahead or below you. You have no idea the position of the controlling obstacle(s).

The AIP states you can commence descent on downwind leg (below the published circling MDA) in order to meet the desired descent profile for the aircraft type. Under the night conditions above, isn't that a bit dicey seeing as you cannot see the terrain below you and you are descending below the published MDA?

[Taggert]

HSWL,

I'll think you'll find that it reads " cannot descend below MDA at night until you are in a position to establish the aircraft on a normal downwind, base or final position in a continous descent at rates of descent normal for aircraft category" . Assuming your circling off an approach, within the circling area and there are no circling restrictions, you should be in no immediate danger.

Tag

[John Citizen]

It shouldn't be dicey if you are flying a normal circuit pattern.

Otherwise the aerodrome wouldn't be there if you couldn't fly a normal circuit pattern there (day or night), otherwise there would be some type of restriction such as :
- right hand circuits on a particular runway
- no night operations ( Wyndham)

[EngineOut]

HSWL,

How else will you get down below the circling minima then??

Seriously...

that is why there are "no circling areas", for night ops and less than VMC. To eliminate the areas that would not provide you with appropriate clearance on a "normal descent profile". You also need to study the spot-height obstacles on the approach chart (that's what they're on the chart for).

[maxgrad]

stay at circling minima until intercept of d/w,base or final using normal angles of bank and descent profiles.

This will, by design keep you clear of obstacles and normally have you descending from MDA once established on finals

[Mango]

Dont forget that you also need to stay within the circling area for the category of aircraft you are in...ie cat B = 2.66nm

[OZBUSDRIVER]

WRT circling area, the old system was 3nm and now we have circling minima for different cat aircraft. Even tho the stipulation has the minima for your particular cat say catA. If the area has been surveyed for upto a catC, would you be safe using the higher cat area even tho it may not be "legal" to use it?

Regards

[Zhaadum]

RE: Higher Cat area.

Good point but as the MDA for Cat C is HIGHER than Cat B and the circling area is also LARGER wouldn't you be is a similar position re gradient of descent? Just a bit higher and further out? More limiting on cloud base and vis too...What is the advantage of it?

[cjam]

It's quite helpful sometimes....and perfectly legal. If you are in a cat b a/c you can maintain msa until you get to 4.2 nm then start your descent down to no lower than the cat c circling minima, then @2.66nm you will be closer to the cat b circling minima. It just means you don't have to dive from msa down to the cat b height when you get to 2.66. Safer this way, lower rates of descent when you are near the ground etc. Most of the time it works out for a normal profile. Correct me if I'm wrong. c ya.

[Howard Hughes]

CJAM,

Can you please clarify this point for me?

If you are in a cat b a/c you can maintain msa until you get to 4.2 nm then start your descent down to no lower than the cat c circling minima, then @2.66nm you will be closer to the cat b circling minima.

Are you saying that you switch between Cat B and Cat C during the approach? If so, I would have to say that I don't agree with your method. You may choose to change categories, but once doing so, the approach must be completed in the newly elected category.

I would also recommend that a constant rate of descent from the applicable fix to the minima, will give you a more stabilised approach with no need to "dive down". All approaches are designed with a constant rate profile which is shown on the chart. (Although you can use the dive and drive method, in the interest of safety and passenger comfort the constant rate must be the best option IMHO)


Zhaadum,

You asked:

More limiting on cloud base and vis too...What is the advantage of it?

The one major advantage is SPEED!! and lots of it!!

Cheers, HH.

:ok:

[cjam]

heh heh, yeah tidy work HH....I was pretty tired when I wrote that and missed the fact that you guys were talking about an actual published approach. For some reason I was picturing in my mind a night visual approach and ensuring terrain clearance, just using the circling areas to gaurantee it. Does that make more sense to you now?

Zhaadum: like HH said, speed is the advantage. Most of the time you know around about what height you are going to get visual at anyway so if it is higher than the cat c circling minima you can smoke it on down at cat c speeds and spend more time eating pies before your next flight.

PS HH, your polite query was appreciated, I am now used to pruners jumping down each others throats before confirming what the other poster meant. Very refreshing!

[Mango]

I would have to agree with HH.

JEP/Terminal/2.1.2 does mention that an aircraft must fit into and be operated in accordance with the requirements of only one category. a) may not reduce category due to reduced operating weight & b) must increase category when actual handling speeds are in excess of those for category based on Vat.

Say you are a cat. B aircraft flying YPAD-ACTIN-W825-YLEC at night. LSALT is 5200, (if you have a TSO GPS for distance) within 25nm its 4700, within 10nm its 3500. I think the correct procedure from this point is to hold 3500 until you are 2.66nm from the field and then descend to the circling altitude of 1710 for a landing say 29.

cjam I dont think that, using the above example, one can hold at 3500 until 4.2nm for catC then descend to 1940 and when you are inside 2.66nm for catB keep on going down to 1710?

Please correct me if I am off the mark here.

[Will Robinson]

Mango

A circling approach is conducted when visual at the end of an instrument approach proceedure, so if you were conducting a dme arrival at night then yes you could circle at the circleing mda within the circling area for your catagory but you cannot decend below the mda untill as mensioned before, that you meet the profile and decent rate requirements. If you have arrived visualy in the circleing area by decending to msa, then no you cannot decend to mda as you have not carried out an instrament approach and must maintain the mda/circuit alt (wichever is higher) untill you meet the decent and profile requirements. I think all this came about from the Young incident with the chieftan.
An operator who has a car217 check and training system can operate in a different catagory withe the approval of casa.

Hope this makes it as clear as mud for you and please excuse any spelling ect. as I now have a wopping headache and am off to find some panadol

Will.

[OZBUSDRIVER]

Zhaadum

Thanks for that. A lesson well learnt. I just looked at first DAP I come across for EN and A & B circling is 1010 C is 1440 and D is 1510.

Regards and Thank You

[cjam]

Mango:

Are you talking about a visual approach to an airport at night? (maybe you and I are the only ones that are...oops) . If you are then it is fine to use the circling minima of all the catagorys because all you are trying to do is gaurantee terrain clearance while you are visual on the airport.
Using the figures you gave, and doing it the way you suggest you will be at 3500ft until 2.66nm, in order to descend down to the cat b circling minima you will need to lose 672ft per nm (more than twice a standard descent profile), thats about 1350ft/min at 120kts, and even that is using the whole 2.66 and not reaching the minima as you enter the circuit, its to reach it overhead the dme. (I dont know the elevation of the fireld you are using).
If you start your descent from LSALT 3500 at 4.2 nm you need a ROD of 426ft/nm (much closer to the standard 300ft/nm), you will be about 2800ft at 2.66nm which is still well above your 1710 ft required and a lot better than still being at 3500ft.
For the record I agree you cannot change cat type half way through a 'published instrument approach' and should use only the minimas for that cat.

Will:
If you have arrived visually in the circling area by descending to msa, you can descend to the circling minima.If you are on a visual approach , all you are doing is maintaining terrain clearance by whatever method you see fit. Hope I haven't got the wrong end of the stick, cjam ps I think there may have been a headache induced typo "descend to mda" as opposed to "descend below mda"

[Mango]

cjam & Will Robinson I should clarify that I am referring to visual approach at night and not instrument approaches.

At 2.66nm CAT B aircraft can descend from LSALT/MSA to the MDA=OCA.

During visual circling descent below MDA may occur when the aircraft is maintained within the circling area. Thus for a CAT B a/c that would be 2.66nm from the field and using the YLEC as an example 1710' is the circling altitude that will give you the 300' obstacal clearance required for CAT B or in other words the MDA. Because after leaving the MDA one has to do a continuous descent to the landing threshold using rates of descents and flight manouvers normal for that aircraft and during descent maintain an obstical clearance along the flight path not less than the minimum for the aircraft performance category until the aircraft is aligned with the runway. Bit of a mouth full but I hope its clear :ok:

[Will Robinson]

Mango and Cjam

Need just a little more info.

IFR or VFR plan.

I read the jepps as saying if you are flying at night VFR (no instrument proceedure has been commenced) then using the circling MDA is not an option. I only have jepps and a referance you can read is Terminal 3.16 Page AU23. Nice little drawing fig IAP 3.8 also dipicts the concept of circling and it is also described in 3.13.3. Effectivly in night VFR your MDA is your LSALT/MSA/circuit Alt within 3nm and your minimum terrain/ obstacle clearance is 500ft assertained from TOPOGRAPHIC charts of the area.

Will.

ps. . Also a notable warning is in 3.13.2 wich is the reason for not decending.

[DeltaSix]

OR........ after you get to the MDA, start wearing your night vision goggles instead......... :} . and go straight to final.... :} :} :}


I heard the US Army helo pilots wear these during night landings..... wonder if fixed wing pilots do as well ?


D6

[Howard Hughes]

Does that make more sense to you now?

It sure does!!

HH, your polite query was appreciated, I am now used to pruners jumping down each others throats before confirming what the other poster meant. Very refreshing!

No worries mate, I like to think of D & G questions as a place where we can all come and learn something from our peers, and maybe occasionally help someone else out.

I think its time for a BIG group HUG!!;)

Cheers, HH.

:ok:

PS: I want night vision goggles too...:8

[Centaurus]

Interesting points made by everyone. Take Canberra for example. Black night runway is clear as a bell, but no way can you see the hills or your height above individual hills because its night. AIP warns against using spot heights for obstacle clearance. Cat C circling MDA is 1684 ft above aerodrome reference point. That is a real high circling MDA because of hills surrounding the airport. It is misty and the viz is 4 kms.

Obviously to execute a stable three degree descent profile and keep within the 4 kms visibility in order to keep the runway in sight on downwind base and final, you would have to commence leaving the MDA on the downwind leg (just like AIP says you can).

As HSWL says its black and you cannot see the ground below you - only the runway lights.

Once you leave the protected altitude which is the published circling MDA, am I right in saying you become responsible for your own terrain clearance? Where is the most critical obstacle within 4.2 nm that gives you the required 400 ft obstacle clearance for Cat C circling? Have you got time to drag out a WAC or Military Survey chart to plot the position of the critical obstacle? Of course not.

The fact that you set up a three degree profile to the threshold plotted backwards up the intended flight path from downwind or early base certainly does not mean a thing when it comes to obstacle clearance. At night can you visually judge 400 ft above terrain on a pitch dark night with no celestial light meaning no horizon? Try it.

Even AIP states that the night azimuth splay is normally increased to 30 degrees to permit T-VASIS to be visible on base leg BUT that obstacle clearance IS NOT GUARANTEED (sorry about the capitals) until the aircraft is within the runway approach obstacle limitation surface. It also states that the T-VASIS should not be used for approach slope guidance until aligned with the runway.

So if Air Services say the VASIS will not guarantee a safe profile above obstacles until on final, what on earth is the aircraft doing descending below the MDA on downwind or base at night where obstacle clearance is not guaranteed below the MDA. Why have a MDA at all if your descent is predicated on a profile rather than height above an obstacle surface.

Clearly it is dangerous to commence descent below the circling MDA until you are established on final on the VASIS or as the AIP says - within the runway approach obstacle clearance surface.

[cjam]

MANGO and Will,

I don't have those books available to me at the mo 'cause I am not flying in Ausi. It seems to me that you guys are trying to figure out what to do by reading the books and then doing exactly as it says. If I am off the mark and you guys have plenty of night approaches under your belt/s then I appologise. If I am right, then I reckon you should not so much read the book and only do as it says, you should look at all the different means of ensuring you don't run into a hill or a chimney etc while trying to get from LSALT to the runway......as well as read the book. Does it specifically say that you cant do it? Nah.
If you are not on an instrument approach then use everything available to you to keep you above obstacles and at the same time avoid high rates of descent when you're low.
If a plane going 160kts is clear of obstacles at 1900 ft within 4.2nm , then a plane doing 120kts will be too.
Keep an eye out for 'no circling ' areas on the maps.

Cheers

P.S.

I\'ll be in for the group hug but only if it is not rhythmic.

[Will Robinson]

Cjam

I do have a fair number of black night approaches under my belt(not sure i should say that around here) and I have to point out to people all the time exactly what you are saying, think about the best way to get to the runway before you get there, wether that is an instament approach even though it's VMC, a dme decent untill in the circling area or a visual approach into the circuit as all have their advantages and disadvatages. Their are some peculiareties to aus rules so some may be different to were you are, but most are there for a good reason. Reading your books and knowing these rules will lead hopefully you to the best decision under your current conditions. A good example is the question given about a visual aproach without having commenced an instument approach, you can only start your decent from msa/lsalt within 3 nm and then the aircraft must be flown to the vfr and that means not lower than 500ft above obstacles and 5000m vis on a vfr plan but if on an ifr plan it would be the circling area and it's obstacle clearance. That ifr chart you have with you is not so flash when it comes to obstacles and terrain so if you at least start an aproach it will be taking you on an initialy safe path untill you discontinue. If your flying in flat terrain and you are familiar with the airports then there is the temptation to cut a few corners and save a few dollars, but when you have the tea and bikies session with casa or th cp after you have been reported by your fo or another aircraft/person then it won't be worth it, that was if you missed that hill that wasn't marked as a spot height as the instrument approach chart you looked at to get your heights because the designers didnt consider it to be a main hazard to an aircraft that was doing an approach.

Having said all that I am certainly not having a go at you or anyone else, just putting my view out their.

Cheers

Will.

ps. In the aircraft I fly we can fly cat C. circling even though its cat B. just to get a bit more room and maintain more speed and this will on ocasions make a visual circling aproach a lot easier wile remaining within the rules.

[Howard Hughes]

you can only start your decent from msa/lsalt within 3 nm

Gidday Will, is this not 5nm?

Cheers, HH.

ok:

PS: DANGER, Will Robinson, DANGER....;)

[Will Robinson]

Hi Howard

I think you will find that 5nm is the size of the ctaf and 3nm is the NVFR circling area based on the aerodrome reference point. Our rules are complex and it's hard to find things at times and sometimes you may find somthing that semms contradictory, so there maybe something I have missed as I havn't flown to the VFR for years. A reference i can give is jep a.t.c. page au601 section 1.4.2 para c & d.

Cheers

Will.

ps. the last time someone said "DANGER Will Robinson " to me it was Woomera.:{

[Victor India]

It's been good to read all of the different ideas and understanding of the rules. I have what I consider a reasonable degree of experience flying night approaches under the VFR and the IFR in aircraft ranging from piston single to heavy multi-engine turboprop to twin engine jet.

The ideas I'm voicing here pertain particularly to the IFR Night Circling Approach (for example after becoming visual off an NDB or a DME arrival).

There have been various comments regarding the point at which descent below MDA is commenced, and the subsequent terrain clearance requirements. Without wanting to rub people's noses in it, I'll need to reiterate a couple of references from AIP...

ENR 1.5 para 1.7.2 states that the spot heights on IAL charts do not necessarily indicate all obstacles or the highest obstacles in the circling area. It also states "Before commencing an instrument approach, pilots should familiarise themselves with the location and altitude of obstacles in the circling area by studying an appropriate topographic map".

ENR 1.5 para 1.7.3 d) "by night or day...intercepts a position on the downwind, base or final leg of the landing traffic pattern, and, from this position, can complete a continuous descent to the landing threshold using rates of descent and flight manoeuvres which are normal for the aircraft type and, during this descent, maintains an obstacle clearance along the flight path not less than the minimum for the aircraft performance category until the aircraft is aligned with the landing runway" (deep breath!!!)

The main opinion which I'd like to voice is based on the red bits above. Just because you have circled on the correct side of the field (away from any published no-circling areas) does not mean you can assume a normal base turn point, base ground track and glidepath will keep you clear of obstacles. The rule says you must maintain at least the minimum obstacle clearance (300' Cat A/B or 400' Cat C) until on final. To do this, you MUST have studied a topo (as is clearly stated in para 1.7.2 above), imagined where your downwind/base flightpath lies and had a think about how you will maintain this clearance until on final. If it means flying a modified ground track or glide path until on final, then do that (within limitations of the aircraft type). A standard base turn will not ALWAYS work.

An example is a right hand circuit to runway 17 at Canberra (there is a "no circling" restriction outside 4nm west but many Cat C aircraft operate normal circuits inside 4nm). Trying to fly a standard profile in almost any aircraft without regard for Mt Ainslie and Mt Majura (both clearly marked on the VTC) would be suicidal. Clearly preferable to fly a left hand circuit but a right hand circuit is possible and requires particular awareness of the terrain even though not included in the "no-circling" area.

Lots of words I know but any more comments? :ooh:

[cjam]

WILL:

Mate that sounds like a silly rule to me....you bloody ausi's I don't know.(jokes).....so let me get this straight, if I was in a barron on a nice clear (very black) night approaching an airport on a vfr plan I would have to wait until 3nm before descending....but I could do another approach exactly the same later that evening except that I am on an IFR plan and so now what? I can descend at 2.66nm or 3 or 4.2? It all sounds like poppy-cock to me, too confusing. If there are no 'no circling' areas I think I will start my descent at 4.2nm. Next thing you are going to try to tell me you cant join straight in and have to do three legs of the circuit or something equally crazy.....

[Howard Hughes]

Thanks Will,

I stand corrected, you are indeed right. :ok: It's amazing what you forget when you don't use it!

I think where I was getting confused is Jepp AU-706 1.9.9.5

until the aircraft is:

within 5nm (7nm for a runway equiped with an ILS) of the aerodrome, aligned with the runway centreline and established on the T-VASIS or PAPI.......etc, etc.

This is the procedure that I use if I have not conducted an instrument approach.

Cheers, HH.

:ok:

[Will Robinson]

Victor India

Spot on and its good to have those AIP referances for people without jepps

cjam

Yep youv'e just about sumed it up and your gess was right. As Howard says in his next post, straight in approach will require the t-vasi or papi.. ect.

Howard

No worries mate. These questions realy had me thinking too and I have only just completed a renewal with a night sector to a strip that verry much reflects the strips in question (msa/lsalt above circuit alt with a visual approach, remote area) and I still had to really search.

Cheers again

Will.:ok:

[Mango]

Ok, I am interested to see what people say about the following.

Since Canberra is a good CFIT scenario lets use that. Sorry cjam cant include you in this ;)

Say you are flying Sydney-Canberra via SHELLYS (V175) CAT B on a clear night landing on runway 35. LSALT=4900' MSA25nm=4500' but does change depending on your radial (check the plate) MSA10nm=5100nm. To be honest I would track from D20/CB to the IAF via the 13nm arc for an ILS just to be on the safe side every time.

But for the purpose of this topic lets say ATC has gone home, the noise abatement procedures were void and its visual. What would you do to get to runway 35? What hight would you fly at? When would you start descent in the circling area? keeping in mind this topic.

[cjam]

aarrggh MANGO!!!!
Thats simply not fair! I wanna play too. I'm guessing a radar derived dme sector arrival with a half double decaffinated haf caf....close?

[Victor India]

Mango,

I agree – an ILS would be my preference if there is no rush. A night circling approach increases your chances of having a CFIT accident hugely.

If for some reason the ILS is not an option, I would (since you set the scene as a visual night) plan a Night Visual Approach in accordance with those rules in AIP ENR 1.1 para 11.5.5. I have assumed that we’re flying under IFR and that accurate QNH is available from the AWIS. Once inside the circling area (which is pretty much where the visual approach rules leave us), I apply IFR circling rules in accordance with ENR 1.5 para 1.7.2 and 1.7.3.

Descent Profile:

I’d try to plan a continuous descent from the cruising level if possible, being aware of the following descent limitations:

Not below 4900’AMSL (V175 LSALT) until 25DME CB, then
Not below 4500’AMSL (CB 25NM MSA) until the Cat B cirlcing area, ie
2.66nm from the threshold of RW17, then
Not below 3250’AMSL (Cat B circling MDA) until that point on downwind, base or
final which a continuous descent can be made (see my previous post)…

Since the VOR/DME is 0.5 nm north of the RW17 threshold, fixing inside 2.66nm wouldn’t be too hard. 1.9 DME on the 031 radial (V175) would be safely inside Cat B circling. Refer to the airfield diagram if required.

Tracking:

I’d maintain V175 inbound until within the Cat B circling area, then turn left as required to join downwind then fly a right hand circling approach as required by ENR 1.5 para 1.7.3 d). Alternatively, keeping in mind that we should fly a left circuit when it’s MBZ, overfly for a left hand circling approach.

Not that you’d need it in this case, but if the 25nm MSA was a lot higher and/or the descent profile inside the Cat B circling area was too steep, I’d consider stepping down using the Cat C circling area and MDA at about 3.6DME (4.2nm RW17). I know it’s safe but you need to be happy the that the visual approach rule can be interpreted this way before you do it in a Cat B aircraft.

Hope this helps.

VI

[Will Robinson]

Mango

Exelent question.

the ILS would always be my prefered option followed by the next most accurate approach at night before considering a visual approach in such a high cfit situation, but for the purpose of your question i'll consider a visual approach, cat b, ifr plan.

decend on v175 from shellys to 5100' and go for a right downwind within the circling area of 2.66nm, probably around 2nm at aprox 1nm befor the threshhold of 35 start a decent around 600fpm and this should place me abeam disaster hill at aprox 2600' wich is above the sugested limit of 2400' from there it should still be a 600fpm rod to the threshold with a normal turn onto final.

I have no topo charts of this area and i am totaly unfamiliar with it so I have based my reasoning on the 2nm distance that the dme is from 35 threshholdand, the 4nm circling restriction to the west, the noted terrain and the circling area design based on 2.66nm limt from 35 threshold. If i did a left downwind there is high spotheights depicted as well but if you were at the limit of the circling area you would be at 4.66nm and in the no circling area so it dosn't seem as safe.

Ok thats me done but you seem to have some local knoledge Mango so you may want to fill us in later how it's done down there.

Will.

[Centaurus]

Question for the experts. Scenario No 1. Black night circling approach. Circling MDA 1200 ft agl. Position of critical obstacle unknown except by Air Services chart designer. AIP states you are authorised to commence descent in order to achieve typically a three degree profile from say downwind leg. You leave the MDA mid downwind to follow the three degree profile as per AIP ENR. AS you turn base on three degrees profile you are now 400 ft below the circling MDA but nicely on profile using visual judgement only.

Next scenario - same airport - same MDA - black night etc. You are in and out of cloud downwind and decide to descend below the circling MDA by 300 ft or more in order to maintain visual with runway. No vertical visibility in either case because it's dark. As you turn base you notice that your position is now exactly on the same profile as Scenario No 1. Handy coincidence which is nice.

Is Scenario No 2 safe and legal? If not, why not? Good instrument rating question, maybe?

[Will Robinson]

Centaurus

I would say case 2 is not ok as you will breach the requirement that by night you do no decend below mda unless you can maintain visability along the intended flight path as at the mda you are in and out of cloud and therefor cannot decend any further.

Will.

[OzExpat]

In and out of cloud while circling? :eek: According to Pans Ops, circling is called "visual manoeuvring". The MOC for circling by each aircraft category is intended to provide comfortable clearance above obstacles, especially during turns where - of course - one wing tip will be lower than the rest of the aeroplane and therefore potentially closer to the critical obstacle.

[Will Robinson]

Oz Expat

yes your right OZ, I neglected to ad to the end of my post that a missed approach would have to be carried out.:hmm:

[cjam]

Scenario one sounds good although I don't agree with the
"nicely on profile using visual judgement only" bit. You said it was a black night circling approach, I would use visual judgement only to gauge where I am in the circuit, profile information would come soley from instruments. I would leave 1200ft agl at the end of the downwind and be fully established on finals by 600ft or nail the papis if they are there keeping a close eye on ROD the whole time ie dividing groundspeed by two method.
Scenario two I would take to warrent a missed approach climbing turn towards the runway. If you are in and out of cloud you are obviously losing sight of the runway and ground etc therefore MAP applies. Also with scenario two you are throwing your obs clearance out the window by descending lower than a normal profile....you should maintain MDA until intersection of the normal profile. In this case about three quarters of the way down downwind leg.
Good instrument rating question? Definately, I think discussing this sort of scenario with students will actually get them thinking about how they are going to stay in one piece instead of regurgitating rote learned bollacks.
I think this sort of thread is where pprune excells. I welcome as much constructive critisism of my posts on this as possible....hopefully might learn something. still waiting for that group hug HH....half way through a tray and it's starting to look good!

[Centaurus]

The flight paths as described in the question both coincided in a base leg turn at 400 ft below the circling MDA except that in the first scenario the aircraft left the MDA on the downwind leg in order to meet the desired visual profile for landing.

Scenario 2 also descended below the MDA downwind but for a different reason - and that was to maintain visual reference with the runway. Once the pilot left the MDA downwind (black night, runway in sight, but unable to positively maintain Cat C 400 ft terrain clearance due black night), he entered the danger zone where he became responsible for his own terrain clearance.

Both scenarios were equally dangerous in that both aircraft deliberately ignored the MDA by descending prematurely downwind, but for different reasons. Although the aircraft in Scenario No 1 was fully visual with the runway on the downwind leg, he still delberately elected to operate below the circling MDA downwind and on base. Remember the initial picture was that both aircraft were 400 ft below the MDA turning base and therefore unprotected by the Air Services published MDA of 1200 ft.

Of course, as someone quite rightly pointed out, No 2 aircraft should not have descended below the MDA downwind in order to maintain visual contact with the runway. Once it was clear he was in and out of cloud at the MDA he should make a missed approach.

Yet it seems it is quite OK for aircraft No 1 to do exactly the same descent below the MDA as No 2 aircraft, but in this case to meet a desired descent profile as authorised in AIP.

Notwithstanding the provisions of the AIP with regard to intercepting a "normal" profile for the type of aircraft, in order to make a continuous descent to land from downwind, it should be clear that if this involves deliberately ignoring the MDA, the pilot does this at his (and his passengers), peril.

During the conduct of a night circling approach where visual judgment of height above terrain immediately below the aircraft is not possible, then adherence to the circling MDA or above, is absolutely vital.

Only when the aircraft is aligned with the landing runway should descent below the MDA be contemplated. If this is not possible due to unacceptable excessive descent angle on final then an alternative approach procedure should be made. If that is not available then the pilot should not land.

Pilots should be aware that the wording in the AIP in regard to circling approach MDA and descent below the MDA to meet a desired aircraft profile can be misleading. What is not misleading, and in fact is crystal clear, is the published requirement at AIP ENR 1.5-3, to "maintain an obstacle clearance along the flight path not less than the minimum for the aircraft performance category until the aircraft is aligned with the landing runway". And if you cannot see the terrain you are over, then you have no business descending below MDA downwind or base in order to set up a nice descent profile. All this is about circling approaches at night. Daytime is entirely different, where you can see the ground you are flying over.

[Will Robinson]

Centaurus

I would sugest that if you could not make an approach from the mda using the methodes setout in the regs then the designers would have put restrictions on the charts,ie- no circling ect.

I do agree although that when you go into a strip for the first time at night that it realy keeps you thinking and hoping you've got it right. The worst is probably a remote strip with no moon or background lights and kerro burners :suspect:

Will.

[Centaurus]

I suppose the key to a safe circling approach at night is to accept that the chart designer has done all he can in this respect by publishing the circling MDA.

If the pilot in his wisdom(?) decides that the MDA is for wimps and the object of the exercise is to get the aircraft on the deck, then the next person in the equation is the ATSB to investigate the wreckage. The Chieftain accident in Young, NSW was a classic example. The pilot there steadily descended below the night circling MDA on downwind and base and ended up in a ball of flame. He thought he was safe.

[cjam]

Did the chieftain driver in young decsend below 1000ft agl on downwind? and continue a steady descent on base? Genuinely interested in the answer to that.
Your point is well made centaurus and I have to admit I have always believed that if it is a circling area and you are in a normally spaced circuit then you can descend on a normal profile. I am still not quite convinced that this is not the case as I had thought they would have made it a 'no circling' area if you couldn't descend like that.
I am sure that what you have written from the books is spot on but can you provide an example of an airfield where turning base at 1000agl and making a normal 3 degree descent to the threshold within a circling area results in busting obstacle clearance. If you can then I am going to have to rethink my techniques! Cheers.

[maxgrad]

Don't know the answer to the chiefain Qn.
As a general rule I maintain MDA until turning onto finals, I have found this gives me the required obstacle clearance, and the profile I need to make good a normal approach and landing.
Haven't been to a strip yet that in doing this has caused my profile to be too steep.

[DirectAnywhere]

I can't understand why this still causes so much grief.

By day if you can see the obstacles, you can descend to the OCA. If not maintain the MDA until you can descend using normal rates to position the aircraft for landing, be it downwind, base or final.

At night, maintain the MDA until you can descend using normal rates to position the aircraft for landing, be it downwind base or final.

In other words for a CAT B prop aircraft, MDA = 1500' AGL, start descent on downwind to position aircraft turning base at an appropriate altitude depending on the aircraft position.

MDA = 700' AGL, start descent mid base.

MDA = 400' AGL maintain until established on final.

Whilst it is a visual manoeuvre, it should be flown with close reference to the altimeter.

I think you've obviously thought a lot about your answer Centaurus, and not wishing to belittle you, but I think your fundamental premise is wrong.

As a hypothetical, how would you safely circle a CAT A aircraft at an aerodrome with an MDA of say 1500' AGL if you were not able to descend below the MDA until aligned with the landing runway as you say you would do? In this case an average RoD of nearly 1000'/min is required assuming a GS of only 60 kts - assuming you're aligned with the landing runwy right at 1.6Nm. Pretty hard to do, and do safely, I'm sure you would agree.

One thing this thread does prove however, is how ineffectually the recommendations of the then BASI following the Young accident, have been implemented by CASA. I believe I'm correct, as obviously does Centaurus!! It is apparent that this issue needs to be revisited and the publications clarified further, and further training material published, to remove any doubt as to the correct way to perform this critical manoeuvre.

[cjam]

Direct Anywhere' , I am of the same opinion but if there are examples of airports where doing this will kill you then I will re-think it. I don't think there will be though because the approach planners will have made them 'no-circlining areas.

[john_tullamarine]

Several thoughts ..

(a) the critical obstruction for circling is not published but is available if you track down the right people .. however, one needs to know a bit more about the general set of obstacles in the circling area as there may be only the one significant obstacle .. or there may be a number, of which one is the critical concern for the published limits. Getting this data is done routinely by those of us who play with performance scheduling work as it is useful for OEI recovery planning in the published takeoff procedure for a particular runway. Normal scale topos are pretty useless and relying on the IAL spot heights is foolhardy .. keeping in mind that they may not be exhaustive and reflect ground rather than clearance heights.

(b) local knowledge is critical for low vis circling approaches. If you know the runway well and can positively locate yourself throughout the exercise, clearly the situation is much more comfortable than if you have never been to the place before.

(c) many pilots on their first trip to an aerodrome in other than day VMC conditions will ALWAYS shoot a published runway letdown (where available) to remove a bunch of worries from the immediate flightpath management considerations.

(d) having frightened myself in earlier years in that, after arriving at an aerodrome for the first time in the dark and then looking at it in the harsh reality of the next day's light .. I will choose not to wing a circling approach unless I can work on the basis of descending on final .... conservative perhaps but comforting .. CBR is a good example and I never really liked running down the approach to 17 in the dark and seeing the lights above us to the side ...

[Centaurus]

Pertinent extracts from the ATSB report on the Piper Chieftain accident at Young NSW,which killed all on board:
Paragraph 2.3 (f):
"At night in the absence of extensive ground lighting or other means of seeing the ground or water, the investigating team considered that descent below the minimim circling altitude is not practicable until the aircraft is aligned with the runway to be used."

Paragraph 3.2: "The aircraft descended below the minimum circling altitude without adequate monitoring of obstacle clearance by the crew, and the visual cues available to the flight crew were insufficient as a sole source of height judgement."

"The flight test at night replicating the flight of VH-NDU suggests that a pilot could not visually assess aircraft height over obstacles along the flight path of the aircraft during a right downwind or turn on to base. The crew of the test aircraft reported they were unable to ensure adequate visual reference along the flight path during downwind and turn on to base."

I recommend that readers examine the various approach plates for Mudgee, NSW as an example of a high circling MDA. In this cae it is 1975 ft above aerodrome level for a Category C aircraft and 1485 ft AAL for category A and B. Circling to the west of the aerodrome is permitted but if the visibility is at the circling minima in either case, it would be almost impossible to land due to the high angle and rate of descent required if descent below the MDA is delayed until established on final approach.

Therefore an early descent starting at downwind and continuing on base would be needed in order to maintain a normal descent profile. There is no guidance on the various approach charts at Mudgee to indicate the critical obstacle therefore it's position in the circling area is unknown except to the chart designer.

The dangers involved with descending below the circling MDA in order to meet a desired descent profile is graphically described in the earlier quotes by ATSB in relation to the Chieftain fatal accident at night at Young, NSW.

Mudgee is therefore a good example of where a circling approach at night is hazardous and should not be attempted in visibility at the circling minima. Mareeba in North Queensland is another example where in this case the VOR approach plate reveals a circling minima of 1700 ft above aerodrome elevation with 2.4 kms vis limit for category A and B. Potentially deadly at night.

From all this emerges one stark fact of life and that is you should never contemplate going below the circling MDA at night until you are aligned with the landing runway. If you cannot land safely because the final approach is too steep - then stiff! Divert to your alternate.

[cjam]

Thanks for that centaurus. I see that the investigation chaps recomoend staying up at mda until finals but I still suspect that that pilot went below a normal circuit profile. Same with Mudgee, if you started your descent from 1500ft half way along downwind and kept it at 3 degrees..monitoring ie not below 1000ft on downwind and established on finals by 600ft...would you bust obs clearance? thats the only question really and I don't believe the planners would leave it as a circling area if you did.
Cheers

[DirectAnywhere]

Just a couple of issues with your post regarding the Young accident Centaurus.

The aircraft initially impacted trees, while on a right base for the aerodrome, at a straight line distance from the threshold of 2215 metres. These trees were at a height of only 275 feet above the threshold elevation which indicates the aircraft was grossly low for a normal approach at the time - obviously. It indicates that little regard was given to flying a normal approach path. Had the aircraft been at a normal altitude at this time with roughly 2Nm to travel to the threshold, it would have been some 800' above threshold elevation, or 500+ feet above the terrain, and there would have been no issue.

Also, in this case, the PIC, once visual, deliberately descended to 2000', some 400' below the circling minima and some 750' AAL to maintain "visual". This was not at a point in the circuit where the aircraft would intercept a normal approach path - hence the subsequent change in the documents.

Not forgetting also the Captain's RMI and HSI were U/S forcing the Captain to scan across to the FO's instruments. It is considered "likely" that the final descent to 275' AAL was unintended and may have gone unnoticed. This cannot be defended against if both crew miss it.

The PIC was also not qualified for the route to be flown and had not been checked in to Young.

Based on your commentIf you cannot land safely because the final approach is too steep - then stiff! then you should not be at the airport in the first place! It should be determined preflight that this approach will be too steep to allow a safe descent when the aircraft is aligned with the runway and the aircraft should not be flown there at night.

Try telling that to any Chief Pilot when the AIP gives adequate guidance to safely conduct a circling approach, when adequate consideration is given to the terrain within the circling area.

John_Tullamarine's advice is good advice. I would not want to turn up somewhere for the first time at night, in IMC, and attempt to circle without having a good idea of the terrain below me. That said, I am happy, having been there before, and given adequate consideration to the terrain, to descend in accordance with the AIP.

Subsequent amendments to the AIP have cleared up many of the issues identified during this report. I still believe the 300/400' is not relevant at night with respect to visual clearance, provided an adequate study of the terrain has been made - and no that doesn't merely include reference to the aerodrome diagram and approach plate. Out of interest, isn't it about time the chart provider gave information on those obstacles or is it merely another case of bureacratic arse covering at the expense of flight safety?

[cjam]

Thanks 'Direct Anywhere', that clears up what happened at YOUNG for me. Can someone with access to Mudgee plates answer my second question which was
"if you started your descent from 1500ftagl half way along downwind and kept it at 3 degrees..monitoring ie not below 1000ftagl on downwind and established on finals by 600ft...would you bust obs clearance?"

With respect to the young accident, does anyone think that working out AMSL heights to be at turning base and turning finals, prior to being there, is important? It is something I like to do. Even though the calculation is simple I find it reassuring to have done it with no pressure so that when the workload is high I have faith in those figures.
Is it possible that in the YOUNG accident, with a high workload situation that SA was lost with respect to height agl because of the height above sea level?
Cheers

[Centaurus]

How many times does one have to repeat the mantra before it sinks in. If you cannot see the terrain below you because it is too dark (read the ATSB report on the Young accident) then never go below the MDA at night until you are aligned with the runway. Even ATSB says that.

The so called profile descent discussed in both AIP and in previous posts has absolutely nothing to do with obstacle clearance on a night circling MDA. Once you decide to fly into the No Mans Land below MDA at night, then you put yourself and your passengers at significant risk of running into a rock sticking up from the terrain you cannot see. This is especially relevant at some overseas airports where the circling area is much smaller in design than Australian airports.

The profile is an aircraft type thing, and the chart designer couldn't care less if the pilot chooses to fly inverted on downwind and base during the whole procedure - or indeed whether the pilot calculated descent "profile" flown is a three degrees, six degrees, or even a helicopter ninety degree descent vertically. It will never guarantee you obstacle clearance - only the MDA will do that for you which is why the chart designer publishes it for all to see. The old adage: "There's none as blind as those who will not see", comes to mind here.

Having said that, a vertical helicopter descent from the circling MDA situated directly above the landing threshold ie a 90 degree profile, is probably the safest way of descending below the circling minima on a dark and stormy night. But then helicopters frighten the hell out of me

[OzExpat]

I did my first 100 instructing hours at Mudgee (and quite a few more than that, later in my career), with many hours in the circuit at night. Having flown there so much by day and night, I was comfortable in establishing a normal circuit height on a close mid-downwind, with normal descent on base to setup a normal final approach.

That was before VASIS, but not before I was very familiar with the place. I wouldn't do the same thing on a first-up visit somewhere else, with similar challenges. There is simply no substitute for local knowledge for those black-hole approaches at night.

cjam... there are places here in PNG where the designated "no circling" area is only marginally worse than the area that's available for circling. Many of the places, where night operation is permitted, are complete black holes (ie no ground lights anywhere except the runway itself).

As part of the job that I've held for a total of 14 years so far, I design instrument approaches in PNG. I can tell you that there are many instances where the "critical obstacle" is only minimally higher than other obstacles, so it does not improve safety to simply identify that one obstacle. And it's impractical to identify all of the obstacles.

Here, perhaps even more than most places in Australia, local knowledge is everything. This is as true of day operations, when the weather is marginal, as it is of night operations in any weather conditions.

[cjam]

ok I'm getting the idea that some experienced pilots out there would be uncomfortable with my take on what is safe with regard descending below MDA within the circuit and on a normal profile. I am all for adjusting ones ideas and am contemplating refining my take on this.
That said, I would still like an answer to that Mudgee question even if it is just to confirm that I need to rethink my approach.
the question for all you folks with access to Mudgee maps and plates;
"if you started your descent from 1500ftagl half way along downwind and kept it at 3 degrees..monitoring ie not below 1000ftagl on downwind and established on finals by 600ft...would you bust obs clearance?"

Also, can anyone think of any airport (NZ or Aus) that has a circling area in which obs clearance would be busted by descending on a normal 3 degree profile, within a normal circuit .
Cheers

[swh]

Cjam,

Cairns, Ballera, Strahan, Ballina, Kununurra, Cobar, Coffs, Cooly, Learmonth, Brewarrina, Cooktown, Dysart, Paraburdoo, Barimunya, Wyndham, Bronzewing, Jundee, Argyle and Rottnest Island come to mind.

Some aerodromes like Wyndham require CASA approval to operate into at night, or dont permit normal night operations like Rottnest.

I just think circling at night is silly esp with the number of runways aligned approaches available.

:ok:

[NOtimTAMs]

Ballina?

All circling is to the south (RH CCT RWY 06) with no significant obstacles and plenty of ground lighting; circling MDAs are 780'. Perhaps you are thinking either of somewhere else - or you too have witnessed the occasional Dash-8 and 737 do LH CCTs onto 06 in contrvention of ERSA (not to mention the direct entries onto base in the circuit by the Saabs)

[swh]

NOtimTAMs,

Nope thats the one, think somthing about 600 ft just to the north of the 06 approach.

:ok:

[cjam]

swh,
I have been thinking about those runways and all the ones I have been to (three)are not answers to my question. I am starting to think that there are no airports where...
if you started your descent from 1500ftagl half way along downwind and kept it at 3 degrees..(monitoring ie not below 1000ftagl on downwind and established on finals by 600ft.).and you are in a normal circuit within a circling area, you would bust obs clearance.
I guess you missed the bit about being in a circling area or something swh, Please can someone give me an example with some figures ...how much do you bust obs clearance by? cheers

[NOtimTAMs]

SWH

...ummm, that's one of the reasons the DAPs show "no circling" to the north of the runways at YBNA. Ain't no obstacles of any note in the permitted circling area.

;)

[DirectAnywhere]

Centaurus, I just think we're hoing to have to agree to disagree. You're still here, I'm still here so neither of us have hit any hills yet.

The BASI, it wasn't the ATSB in the days this report was written (1993), clearly advocated maintaing the MDA until aligned with final. That said, it's worth noting the significant amendments, in the ensuing 12 years, with respect to circling, to the then AIP DAP IAL and current AIP ENR.

These documents have not remained static over the last 12 years. It is my firm belief, that these amendments completely change the intent of these documents. The current documents simply do not allow an aircraft to be at 275' AAL on early base in IMC or at night. The old documents didn't either but were so poorly written it was a common misconception.

These poor people were the victims of serious organisational failures within the then CAA - that ultimately resulted in its breakup to form CASA and AsA, and Monarch. In additon poor maintenance and poor check and training standards were also identified.

I respect your view but we're going to have to agree to disagree.

SWH, Cairns has got a lot of big hills but so long as you remain inside the designated circling area - east of the field and north of Trinity Inlet, there's nothing to run into. I believe this is one of CJAMs and my main conjectures.

[swh]

cjam,

Your question was "Also, can anyone think of any airport (NZ or Aus) that has a circling area in which obs clearance would be busted by descending on a normal 3 degree profile, within a normal circuit ."

I gave you an answer to that question, the airports I listed have circling areas, they also have obstacle clearance issues, the designated IFR circling area may not be permitted within the "normal circuit" of the aerodromes I previously listed.

If it didnt answer the question you wanted, could you pose the question differently to get the answer you are seeking.

Also can think of many "no-aid" aerodromes which also have a circling area which have a "normal circuit" which also have obstacle clearance issues.

:ok:

[Victor India]

This post seems to spark up enormous debate and the variation in opinion probably is evidence that the current AIP rules still lack enough guidance for some readers. Nonetheless – I have no gripes with the rules as they stand and believe I am safely conducting night circling approaches (when absolutely necessary) including descent below MDA prior to reaching final.

I posted a reply on page 2 of this thread (21st Apr 01:10). I think a couple of points from that reply could do with reiteration…

Centaurus:

Re: Your reply on this thread on 20th Apr 18:47 (page 2 of this thread). You asked:

Once you leave the protected altitude which is the published circling MDA, am I right in saying you become responsible for your own terrain clearance?

Absolutely. AIP ENR 1.5 para 1.7.2 states "Before commencing an instrument approach, pilots should familiarise themselves with the location and altitude of obstacles in the circling area by studying an appropriate topographic map".

Based on this rule, your comments immediately following your question concern me a little:

Have you got time to drag out a WAC or Military Survey chart to plot the position of the critical obstacle? Of course not.

In a later reply (22nd Apr 23:38, page 3 of this thread), you state:

Notwithstanding the provisions of the AIP with regard to intercepting a "normal" profile for the type of aircraft, in order to make a continuous descent to land from downwind, it should be clear that if this involves deliberately ignoring the MDA, the pilot does this at his (and his passengers), peril.

Well – I would tend to agree if you are going to ignore the AIP rule of making reference to a topographic map as required by para 1.7.2 above. THIS RULE IS CRITICAL TO THE SAFE CONDUCT OF NIGHT CIRCLING APPROACHES.

If a topographic map of the airfield is available, the obstacles surrounding the airfield should never be known only to the approach designer.

The approach plate is an INSTRUMENT APPROACH plate designed to safely get you to the minima (hopefully) before the MAPP. From there, the pilot needs to have done some solid homework with a topo regarding the terrain before flying a night circling approach. No – I would not expect someone to do this airborne – this is a preflight preparation task. During the approach brief, the topo can be revisited briefly to refamiliarise oneself with the orientation gained during preflight preparation. Your method of maintaining MDA until on final, whilst seeming to be on the safe and conservative side of the rules, may in some cases lead you to require a high rate of descent on final after just flying over possibly flat and featureless terrain on downwind and base. Seems a bit silly and a less safe approach overall.

Then again – if during your preflight study of the topo you had identified an obstacle under the base turn flight path which would infringe your expected glidepath by more than 300’/400’, you might choose to modify your base turn position and/or your vertical profile (rate of descent) to maintain your 300’/400’ clearance until on final when you could then use a slightly increased rate of descent early on final. I have needed to plan and fly such a modified profile on several occasions, although granted I did have the help of obstruction lighting to help me identify the obstacles.

Sorry to harp on but I feel that the need to consult a topographic map has been largely neglected by you and others on this thread.

DirectAnywhere:

Re : Your reply on this thread on the 23rd Apr at 10:36

You mention that the 300’/400’ terrain clearance requirement is inapplicable to the night case.

ENR 1.5 para 1.7.3 d) "by night or day ...intercepts a position on the downwind, base or final leg of the landing traffic pattern, and, from this position, can complete a continuous descent to the landing threshold using rates of descent and flight manoeuvres which are normal for the aircraft type and, during this descent, maintains an obstacle clearance along the flight path not less than the minimum for the aircraft performance category until the aircraft is aligned with the landing runway "

In light of the fairly clear guidance above, I’m not sure where you’re coming from.

CJAM:

You wee requested responses from anyone regarding airfields at which a standard circuit will not work.

Canberra is a classic. Have a look at the VTC and the RW17 VOR plate. Although there is a no-circling restriction beyond 4nm west of Canberra (I think this may be based on Black Mountain Tower), a standard circuit can be flown in almost any aircraft type inside 4nm. Inside 4nm, however, there is some very significant terrain (Mount Ainslie and Mount Majura which is probably the limiting obstacle). The circling MDA for a Cat C aircraft to RW17 is 3530’AMSL on accurate QNH (about 140’ above a 1500’AGL circuit altitude for a jet). If a standard jet circuit is flown with descent just before the base turn point (MDA 1640’AGL), not only will the 400’ obstacle clearance requirement until on final be breached, but the aircraft will probably hit Mount Majura (highest marked elevation 3036’AMSL). Modifying the base turn ground track and glidepath (within circling area and aircraft limits) is required and results in an acceptable circuit. With some local knowledge and good obstruction lighting, I have done this at night but would strongly discourage it without adequate obstruction lighting. Obviously, a left hand circuit is preferable.

Is this what you’re after?


I am really interested to know if people think this topographic map awareness stuff is all hot air.


VI :D

[Victor India]

This thread seems to spark up enormous debate and the variation in opinion probably is evidence that the current AIP rules still lack enough guidance for some readers. Nonetheless – I have no gripes with the rules as they stand and believe I am safely conducting night circling approaches (when absolutely necessary) including descent below MDA prior to reaching final.

I posted a reply on page 2 of this thread (21st Apr 01:10). I think a couple of points from that reply could do with reiteration…


Centaurus:

Re: Your reply on this thread on 20th Apr 18:47 (page 2 of this thread). You asked:

Once you leave the protected altitude which is the published circling MDA, am I right in saying you become responsible for your own terrain clearance?
Absolutely.

AIP ENR 1.5 para 1.7.2 states "Before commencing an instrument approach, pilots should familiarise themselves with the location and altitude of obstacles in the circling area by studying an appropriate topographic map".

Based on this rule, your comments immediately following your question concern me a little:

Have you got time to drag out a WAC or Military Survey chart to plot the position of the critical obstacle? Of course not.
In a later reply (22nd Apr 23:48, page 3 of this thread), you state:

Notwithstanding the provisions of the AIP with regard to intercepting a "normal" profile for the type of aircraft, in order to make a continuous descent to land from downwind, it should be clear that if this involves deliberately ignoring the MDA, the pilot does this at his (and his passengers), peril.
Well – I would tend to agree if you are going to ignore the AIP rule of making reference to a topographic map as required by para 1.7.2 above. THIS RULE IS CRITICAL TO THE SAFE CONDUCT OF NIGHT CIRCLING APPROACHES.

If a topographic map of the airfield is available, the obstacles surrounding the airfield should never be known only to the approach designer.

The approach plate is an INSTRUMENT APPROACH plate designed to safely get you to the minima (hopefully) before the MAPT. From there, the pilot needs to have done some solid homework with a topo regarding the terrain before flying a night circling approach. No – I would not expect someone to do this airborne – this is a preflight preparation task. During the approach brief, the topo can be revisited briefly to refamiliarise oneself with the orientation gained during preflight preparation. Your method of maintaining MDA until on final, whilst seeming to be on the safe and conservative side of the rules, may in some cases lead you to require a high rate of descent on final after just flying over possibly flat and featureless terrain on downwind and base. Seems a bit silly and a less safe approach overall.

Then again – if during your preflight study of the topo you had identified an obstacle under the base turn flight path which would infringe your expected glidepath by more than 300’/400’, you might choose to modify your base turn position and/or your vertical profile (rate of descent) to maintain your 300’/400’ clearance until on final when you could then use a slightly increased rate of descent early on final. I have needed to plan and fly such a modified profile on several occasions, although granted I did have the help of obstruction lighting to help me identify the obstacles.

Sorry to harp on but I feel that the need to consult a topographic map has been largely neglected by you and others on this thread.


DirectAnywhere:

Re : Your reply on this thread on the 23rd Apr at 10:36

You mention that the 300’/400’ terrain clearance requirement is inapplicable to the night case.

ENR 1.5 para 1.7.3 d) "by night or day ...intercepts a position on the downwind, base or final leg of the landing traffic pattern, and, from this position, can complete a continuous descent to the landing threshold using rates of descent and flight manoeuvres which are normal for the aircraft type and, during this descent, maintains an obstacle clearance along the flight path not less than the minimum for the aircraft performance category until the aircraft is aligned with the landing runway "

I think that the second part of Note 1 specifically mentions the obstacle clearance requirement because this is an absolute minimum anywhere in the circuit by day only. Since early descent below MDA is not allowed at night, the first part of Note 1 doesn't specifically mention the terrain clearance. I reckon both cases are still covered by para 1.7.3 d) above.

CJAM:

You requested responses from anyone regarding airfields at which a standard circuit will not work due to terrain.

Canberra is a classic. Have a look at the VTC and the RW17 VOR plate. Although there is a no-circling restriction beyond 4nm west of Canberra (I think this may be based on Black Mountain Tower), a standard circuit can be flown in almost any aircraft type inside 4nm. Inside 4nm, however, there is some very significant terrain (Mount Ainslie and Mount Majura which is probably the limiting obstacle). The circling MDA for a Cat C aircraft to RW17 is 3530’AMSL on accurate QNH (about 140’ above a 1500’AGL circuit altitude for a jet). If a standard jet circuit is flown with descent just before the base turn point (MDA 1640’AGL), not only will the 400’ obstacle clearance requirement until on final be breached, but the aircraft will probably hit Mount Majura (highest marked elevation 3036’AMSL). Modifying the base turn ground track and glidepath (within circling area and aircraft limits) is required and results in an acceptable circuit. With some local knowledge and good obstruction lighting, this can be done this at night but I would strongly discourage it without adequate obstruction lighting. Obviously, a left hand circuit is preferable. Interesting though that even if all obstruction lighting is out of service, AIP in no way removes our option to do a night circling approach. Maybe because we've all looked at a topo... :E

(Here's a link to the RW17 VOR for those without the plate)

www.airservices.gov.au/publications/current/dap/SCBVO01-101.PDF (http://www.airservices.gov.au/publications/current/dap/SCBVO01-101.PDF)

CJAM : Is this what you’re after?


I am really interested to know if people think this topographic map awareness stuff is all hot air.

VI :D

[DirectAnywhere]

Oops, meant to delete that bit, VI. Bodgy cut and paste job from the net by me followed by putting mouth into action before brain.

As far as I'm concerned, the first part of your post hits the nail on the head.

BTW, try this link, broken link in VIs post.

CB VOR RWY 17 (http://www.airservices.gov.au/publications/current/dap/SCBVO01-101.PDF)

[cjam]

VI,

That is exactly what I am after and I don't mind admitting I am surprised that it exists. I have no charts etc for Aus but it sounds to me like there is a hill at 1100ft above aerodrome level half way along base and within a circling area. Scarey. Is it well promulgated on the approach plates ? Is a modified circuit depicted that would make you think twice before you launched into it? The last thing I brief on my approach briefs is 'terrain' and I generally look at the plate to see any spot heights etc where I am headed, would that pick it up?

That is exactly what I was asking for examples of. Thankyou.
I will take on board your advise with respect topo's and have a wee look at my circling theories.( I normally look at the toppo's for the places I go but not specifically for obs clearance within the circuit)

SWH, yeah my question was not constructed perfectly was it...what I was getting at was, are there any airports where descending WITHIN a deignated circling area, and within a normal circuit pattern, at a normal profile, will bust your obs clearance. I wasn't talking about doing a circuit in an area that isn't designated for circling. The answer is yes by the looks of things.

I can't see why the planners deignate it as a circling area to tell you the truth but I am sure there are reasons. Has anyone been caught out at Canberra?

Are there any other circling areas that have terrain within the circuit area higher than say 500ft aal?....when answering that question I think heights and MDA's etc are needed because some people get confused and list airports that have high terrain that is not in circling areas. It would be good to get them listed on here even if it is just to get an idea how common it is.

This is a good thread that a lot of people may learn from, Cheers, cjam

[Victor India]

CJAM,

I edited my earlier post today to include a link to the Canberra VOR17 on the Airservices Australia site.

As I mentioned earlier, the spot height of Mount Majura is 3036'AMSL. You can see this spot height a couple of runway lengths (approx 2.5-3nm) north of the field and just west of the extended centreline - under a normal mid base turn position (and well inside the allowable circling area).

You can also see a 3311' spot height (Black Mountain Tower) about 5nm west of the field which I believe drives the circling restriction outside 4nm.

I have checked all documents and none make mention of any special circuit procedure to be followed for right circuits onto RW17.

Another such case which comes to mind is at Townsville (YBTL). Here's the ILS RW01 plate:

http://www.airservices.gov.au/publications/current/dap/BTLII01-102.PDF

On this plate, there is a 671'AMSL hill (Mt Louisa) on a left base for RW01 which is within the allowable circling area. Most aircraft will turn base outside or inside but not directly over this hill. There is a note in the Enroute Supplement Australia which states:

RWY01 T-VASIS use during night hours - Pilots are advised that MT Louisa can infringe approach path for left base RWY01 if aircraft is below on slope indication of the VASIS.
Interesting since we're not meant to use the VASIS for guidance during the base turn...

Also, at Wollongong (YWOL) there are multiple masts up to approx 600'AGL within the allowable circling area which can require a slightly modified base turn profile. Here's a link to the NDB plate:

http://www.airservices.gov.au/publications/current/dap/WOLNB01-101.PDF

The Enroute Supp entry for Wollongong states that RPT or >5700kg need approval from CASA to operate there at night. There is a fair amount of terrain around (to the west), quite poor airfield lighting and dodgy PAL but I'm not sure exactly why this restriction exists.

It seems in some cases, there are notes in the Enroute Supp directly (or indirectly) indicating terrain problems in the circling area, but Canberra - the most severe in my opinion - escapes any comment. Curious.:ooh:

I'll let you know if I come across others.

VI

[Centaurus]

Victor India. Funny thing about studying a topgraphical map as preparation for the possibility of a night circling approach. You are dead right it says so in the AIP. Here is the puzzling part, though. I have never ever seen pilots undergoing an instrument rating test in the simulator drag out a topo from their briefcase and pre-plot a circling approach even though the test is conducted by an airline CASA FOI.

For some reason they rely almost exclusively on the instrument approach chart circling MDA. The CASA FOI's seem happy about that.

Guess it must be too hard to read all the terrain hachures, contours and coloured tints on the topo and almost impossible to remember all that vital info off by heart. In any case I doubt if too many airline pilots with their glass cockpit whizz-bang FMC's bother about carrying a set of topos in their nav bags.

[swh]

Centaurus,

Its the operators responsibility (An operator must not permit a pilot to act in the capacity of pilot in command of an aircraft engaged in) under CAR 218/219 to esure that the PIC has " an adequate knowledge of the route to be flown, the aerodromes which are to be used and the designated alternate aerodromes, including a knowledge of:

(i) the terrain;
(ii) the seasonal meteorological conditions;
(iii) the meteorological, communication and air traffic facilities, services and procedures;
(iv)the search and rescue procedures; and
(v)the navigational facilities;
associated with the route to be flown;"

For RPT CASA approves and directs how this is done. While a PIC may not pull out a topo in flight, they might have a part of the airline which does look into this, may produce special procedures, and produce manuals for flight crews.

This brings a standard approach to looking at risks associated with each port. Any organisation that is smart would do a risk assessment to any port they go to, terrain would be just one risk factor. To suggest they dont is false.

And a common way I have seen this done is to have a policy that circling approaches should not be done where runway aligned approaches are available, i.e. have an approach allowance at dispatch time so that a runway aligned approach can be made.

:ok:

[Victor India]

CAAP 178-1(1) “Non-Precision Approaches” contains some more information. It is a 20 page document which has the following blurb regarding night circling:

Why are the rules different for day and night?

At night it may not be possible to maintain visual clearance from obstacles even if those obstacles are lit or shown on instrument approach charts. For this reason the rules for circling at night require that the MDA is maintained until in a position where a normal descent can be conducted, and the aerodrome Obstacle Limitation Surfaces (OLS) are intended to enable a safe approach to be conducted in those circumstances. (Refer AIP ENR 1.5 para 1.7.2). However the responsibility for maintaining adequate obstacle clearance still remains with the pilot and caution should be exercised. Descent should not be commenced or continued until obstacles that may affect a safe visual approach from the MDA are identified or passed.
CJAM : It does state that the OLS are intended to enable a safe approach by an aircraft using a normal descent, but then covers itself by leaving the final responsibility for safe obstacle clearance with the pilot.

Centaurus : In your last reply, you said:

Here is the puzzling part, though. I have never ever seen pilots undergoing an instrument rating test in the simulator drag out a topo from their briefcase and pre-plot a circling approach even though the test is conducted by an airline CASA FOI.
I agree with you entirely in never having seen a topo in a sim or a sim briefing. I reckon the reason for this is that there is so much to get through in most of these sims that the preparation is assumed to have been done by the individual pilot, or (since we’re talking about simulators here) by the airline/operator as SWH mentioned above. In all of the circling approaches I’ve done in simulators, the emphasis in the brief has been the appropriate use of automation and flying a stabilised descent, and in most cases the aerodrome used has been on substantially flat terrain.

Given the increased reliability of engines and systems these days and the comparitavely increasing likelihood of CFIT accidents, perhaps sim training could include more focus on the operational application of these circling rules. Then again, with the world push towards straight in GNSS/RNAV style approaches with ILS glideslope style vertical guidance, hopefully these circling approaches will soon become a thing of the past.

You also stated:

Guess it must be too hard to read all the terrain hachures, contours and coloured tints on the topo and almost impossible to remember all that vital info off by heart.
Assuming that your company hasn’t looked at this (maybe you fly a corporate jet without airline style support) and you need to take responsibility, the amount of detail to be recalled in the cockpit isn’t really that great. I generally just have a look at where my intended circuit pattern will take me on the topo (VTC works OK if available), and look for any obstacles which are likely to infringe 400’ (Cat C) during my descent from MDA before I’m aligned with final. I’ll give you an example which I needed to use one night at Wollongong doing a left circuit onto RW16. Have a look at the (Sydney) VTC if you can.

Normally, I’d be rolling out on final at about 700-800’AGL. Just before that, late in the left base turn to RW16 at Wollongong, there is a 436’ mast. That’s reasonably close to breaching the 400’ clearance before I’m on final, so I look to make a simple plan to avoid this. The circling MDA is 1930’ (assuming no accurate QNH) which is 430’ above a standard jet circuit, so I’ll need to commence descent from MDA about the time I pass abeam the landing threshold of RW16. Also, I’ll extend the downwind leg just a little so that, using normal rates of descent, I can limit my descent to not below 836’ (mast height plus 400’) until on final without being left steep on final. Once on centerline (and therefore clear of the mast), I allow descent to continue. If done properly, I would not need to level off at all.

This is all done within the circling rules in AIP and guidance in the CAAP, and results in normal rates of descent and profiles being flown. It only took a couple of minutes to devise.

In reality, flying an accurate standard circuit over the 436’ mast would not infringe the 400’ clearance, but what if I got distracted? (like the Chieftain pilot at Young probably did).

Much nicer to have an awareness of the obstacles and a simple plan to avoid them than leave it to chance!

VI :D

[cjam]

A fair bit of time and effort gone into answering some of these questions, thanks.
I've thought about it a bit and come to the conclusion that I know all the airports that I regularly go into pretty well and am happy with the obs clearance on night circling approaches at these. The area of greatest risk for me would be a divert to an unfamiliar field. It would have to be pretty serious (ie fire) to go to an unfamiliar field, if we are doing that it will be unlucky if we have to do a circling approach ( a bit of tailwind would be preferable to time in the air), and if we do circle, again, it will be unlucky if we strike one of these fields where the OLS doesn't provide obstacle clearance. I will keep it in mind that this is a possibility though and I think that just being aware of these things is half the battle won. I've learnt a bit, cheers. cjam

[CaptainToBe]

I havent read any of the previous posts, but my memory has served me well and this should clarify it for you.

Night
you cannot descent unless youre in the circling area (dependant upon your category af aircraft). this can be extended to 5 miles if the runway has a papi or tvasi and youre not below glide slope. this can be extended to 7 miles if the tvasi or papi is on a runway that also has an ILS, this can be extended to 10 miles if you are on the ILS (visual) and not below glide slope. this can be extended to 14 miles if youre on runway 34L or 16L at YSSY. At all times you must be able to maintain sight of the ground or water (so you cant be between layers), you have to have 5km vis, and you must follow height restrictions (ie, 1000 above populated areas, 500 above non-populated areas). you must also be able to maintain the above conditions.

Day
within 30 miles of airport, be in constant sight of ground or water, follow height restrictions, 5km vis, and be able to maintain the above conditions.

Hope that helps, and i hope i didnt misread the question and look foolish by giving that answer, but if i did, then there a fun fact for you anyway.

[Centaurus]

Captain 2B. I think you are getting confused with the requirements of a visual approach at night, and a circling approach at night from an instrument approach. Two very different things.

The subject of night circling approaches is extremely well covered in Pprune Rumours and News under the heading "Air China 767 crashes in South Korea". Although the crash happened in April 2002, it evoked some very interesting discussions and has been resurrected in a couple of posts this month (May 2005).