Graham Borland

Hello, I'm revising for my PPL Nav exam, and I'm stuck on one of the sample questions in my book. It's asking me to select the lowest available flight level which complies with the quadrantal rule. The track is 063 so it's an odd flight level; the corresponding available options are FL30 and FL50. QNH is 1015.

I had answered FL30, but the book says FL50 is correct. I don't get this.

With QNH 1015, the 1013 pressure level is 60ft above msl. Correct? So, if I'm flying with 1013 dialed in and 3000ft indicated, I'm at FL30 which is 3000ft above the 1013 level, i.e. 3060ft amsl. FL30 is therefore above the transition altitude, so is available for use.

Where have I gone wrong? I hope I don't have a fundamental misunderstanding of this stuff.

The explanation in the book has a confusing diagram with the 1015 level appearing above the 1013 level, which I just can't make sense of.

fireflybob

Firstly I assume that the Transition ALTITUDE is 3,000 ft amsl.

The best way of thinking about this is to imagine you climb to 3,000 ft on QNH 1015 and then parked the aeroplane on a convenient hill at this point. You get out of the aircraft and then reach inside and set 1013 mb. You are winding off 2 mb so that means you and winding off 60 ft. (So the Alt now reads 2940 ft) - You now get back inside the a/c and climb to the next available Flight Level - in this case FL 30. As your magnetic track is in the first quadrant an odd level is appropriate - therefore you may fly at FL 30.

So assuming there are no other stipulations in the question (like a minimum safe altitude for terrain clearance) then I believe your answer of FL 30 is correct.

Hope this helps.

mcgoo

It would be FL50, I don't know what books you have but the Trevor Thom version has a diagram that explains the transition altitude as usually 3000ft and then the transition layer that is 500ft thick usually, but the thickness varies depending on QNH, so adding this on your next available odd flight level would be FL50

PompeyPaul

If you are using "Jeremy Pratt's - Simplifier" then I found a few wrong questions in the PPL NAV section. In fact, IIRC, that question was the wrong one that I found. There is another paper later on that gets it right and contradicts what it is saying there.

For the record FL30 is correct, the book has got it wrong.

Graham Borland

Yes, it's Pratt's Simplifier. The book is adamant that FL30 is lower than 3000ft amsl with QNH 1015, which is just plain wrong.

Glad I'm not the only one who spotted it!

PompeyPaul

Thought I recognised that question. Similarly I was confused took my book up to the flight school and worked through it with a couple of FIs for half an hour or so before we all decided that the book was wrong.

I found Jeremy Pratt's simplifier much more accurate than the "PPL Confuser" by the thai dude though. That seemed to have many more mistakes than Pratt's stuff.

zkdli

Quote "It's asking me to select the lowest available flight level which complies with the quadrantal rule. The track is 063 so it's an odd flight level; the corresponding available options are FL30 and FL50. QNH is 1015."

The question asks for the lowest available flight level. Some basics - the transition altitude outside CAS is 3,000ft. The first fl30 on that track is FL30 and it is also the transiton level. The transition level is not available for use as it does not garauntee any separation from aircraft flying at the transition altitude. Therefore in this case FL50 is the first available FL on that track that provides any separation from the transition altitude.

Graham Borland

I take the point about separation and the transition level. The explanation in the book states, however, that FL30 is below 3000ft amsl with QNH 1015. So, at the very least, the explanation is wrong. There is also no mention of separation, transition layer, or transition level anywhere in the question or answer. It's a simple "which is higher: FL30 or 3000ft?" type question.

fireflybob

Sorry but I do not think this is correct - where does it say that the transition level has to give any separation from the transition altitude? The transition level is the first available Flight Level above the Transition Altitude although from previous threads it seems that somes States do specify this but not the UK - I stand to be corrected!

Take a look at this thread:-

http://www.pprune.org/forums/showthr...ansition+level

DFC

That is wrong.

There is no UK requirement for an aircraft crusing at the transition level to be separated from another aircraft at the transition altitude.

The quadrantal rule does not provide any separation. It is simply an orderly system that can remove some possible conflictions but you can till have an aircraft approaching you at the same level..........from behind, from the left from the right and also from directly ahead! - and that is just the IFR ones who are complying with the quadrantal rule. Add in the VFR flights who ignore the rule and you will see that quadrantal rule and separation should not be used in the same sentence.

The answer is FL30 as this is the first flight level available for use above the transition altitude of 3000ft.

Regards,

DFC

neilmac

I agree with DFC , you take off pressure above 1013(QNH/SAS) thats the golden rule. so assuming 3000ft 1015 , wind off 2 millibars 2940ft therefore round up and you get FL30.

As DFC says it doesnt mean you a sep from other traffic just a means to fly, dont get me going on ATC sep! I try to do it daily!

NM

beatnik

I almost got tripped up with this question when I did my Navigation exam last week. The facts were similar, an "odd" magnetic track per the quadrantal rule - with two possible answers fitting that : FL30 and FL50. If one assumed TA was 3,000ft, then with the QNH given (1015) once you wound off the millibars, the height was 2,940ft. This implied that by climbing a further 60ft you'd be at FL30 -the first available FL. This is also the logic used in The Confuser in most of its answers.

In Trevor Thom's books (pg 123 of Vol 6) he implies that you should have AT LEAST 500ft between Transition Altitude and Transition Level. Applying Thom's logic, you'd have to answer FL50. Now I'm not exactly sure where he gets this from (can't see it in the ANO), but it makes good logical sense for vertical separation from those aircraft flying at 3,000ft not in terms of the quadrantal rule.

Anyway - I answered FL30 believing this is what the CAA wanted, and that turned out to be the "correct" answer (Phew!). I personally believe FL50 is a safer option but clearly this is an area of some confusion. Even the two FI's I spoke to after the exam were unsure.

It's like the confusion with "QNH 1000" in RT speak. Trevor Thom says there is a UK exemption which allows this pressure setting to be pronounced wun-tousand. The editor of CAP 413 disagrees and says it is pronounced wun-zero-zero-zero. (My apologies for thread creep).

http://www.airquiz.com/explain/qnh1000.htm

DFC

G-EMMA,

If you are flying a heading of 270 magnetic (deviation 5W and variation 8E) and the wind from the met office is 180/20. what is the true track made good?.

The nature of weather in the UK is that thunderstorms move from place to place and it is basic knowledge that if there is a thunder storm over your destination or there is soon to be, you hold off for the relatively short period that is required for the shower to pass through.

It's all about demonstrating understanding.

In the USA they use inches of mercury as the altimeter setting. Standard pressure being 29.92

Since the range of pressure precludes a pressure of 39.92, it is usual for the '2' to be dropped and 29.92 is transmitted as 992.

You can se that there is a big difference between a QNH of 992mb and 1013.2mb (29.92 inches hg)

Following from an incident some years back the standard of adding the word "milibars" after all pressure settings of less than 1000mb came into effect to prevent the misunderstanding possible especially with US operators in the UK.

Regards,

DFC

17thhour

This sould clear it all up:

"There would be a possibility of conflict if traffic cruising above the transition altitude were on Regional QNH and aircraft only slightly above it were on the 1013 reference datum. For this reason there is a layer above the transition altitude at which cruising flight should not occur, to ensure satisfactory seperation of at least 500ft."

^^ an extract from the air pilots manual.


Because the transition altitude is at FL30(3000ft), you shouldnt cruise there/in that layer, because aircraft may be on QNH or 1013, making vertical seperation inaccurate.

So im guessing this is the reason that they dont reccomend FL30, but infact FL50... im sure this is right...?

PPRuNe Radar

I will bite ... how can you have an aircraft approach you from directly ahead (i.e. reciprocal) at the same level if you both follow the quadrantal rule ??

VFR traffic is not ignoring the rule ... it does not apply to VFR aircraft therefore how can they ignore something there is no need to comply with

LH2

I hope you're not planning to do any ATPLs then. Six entire weeks are spent on learning what the CAA answer should be! (mind you, saves you from having to know what the actual answer is until after you pass the exams I found it made life easier, in a way)

It is my understanding that steps are being taken in that direction, at least with regards to professional licences. Some of the details can be gleaned by looking at the EASA NPLs. Next comment and response period starts in about a month, I believe, so feel free to chip in if you have any helpful ideas.

For the time being though, from my experience it seems like one should consider passing the exams and gaining the necessary knowledge to fly an aircraft as separate processes. The obvious implication is that one should not make the mistake of thinking that one has the knowledge required to fly safely just because one has passed the exams.

Come to think of it, at the end of the day, the situation is not all that different from gaining a driver's licence.




....oh, by the way, the correct answer is FL50, because it asks for the first available flight level. FL30 is not available for cruising for the reasons explained above by other posters.

Problem is, for each of these questions, there tends to be another version which does not say "available" (in which case of course, FL30 would be correct. Gotta love them )

fireflybob

And what exactly is the "air pilots manual" please?

Ok I presume this refers to Trevor Thom?

Whilst I have every respect for Thom's work not everything you read in a book is correct! It is surely what is specified in legislation and/or the state AIP which is the definitive guide.

llanfairpg

Gemma I think you are missing the point of the Exams. The examinations are not based on what an instructor would do with a student. Think about the situation in say five years time when you are at an airfield in the middle of nowhere and you need to get back home for work the next day. People do alarming stupid things in aircraft which may not be apparent to you at the moment but you wait, you will be posting on here one day "Why on earth did he do that"?

The problem in light aviation is not the exams it is the pilots that think the exams are a problem.

By the way, instructors should not be just telling you they would not be sending students to an airfield with a thunderstorm sitting over it, what they should be saying is they would not be sending anyone on a solo cross country with an unstable airstream with a high percentage chance of showers and /or thunderstorms. Showers and thunderstorms are produced by the same unstable airstreams but it is showers that catch out students (and instructors) more so than thunderstorms. It can be 8/8ths blue at the home airfield and at the destination but a series of showers enroute can turn a VFR flight into a instant IFR flight with dire consequences for students.

The CAA answer as indicated in one of the above posts is above is correct.
This is am arithmetical calculation and problem, treat is as such and one, you will get the correct answer and two you will understand the purpose of the exam.

Spitoon

Focusing on what appears to be a misunderstanding (rather than the pressure level calculations etc.)...
This has been done in the past - many times. ICAO refers to Transition Level being the first available FL above Transition Altitude. The Transition Layer is the airspace between the Transition Altitude and Transition Level - it is of variable depth and depends on the Transition Altitude, prevailing pressure and, in some cases, national rules. In the context of Transition Altitude/ Level/ Layer, ICAO makes no reference to IFR separation or other ATC issues.

The interpretation of the word 'available' varies. To some it means the first 'proper' flightlevel that exist above Transition Altitude, to others it means the first that exists above a minimum Transition Layer of 500ft, yet others want a minimum Transition Layer of 1000ft. All may be valid interpretations if there is no laid down standard for a particular State or piece of airspace.

I've seen some States set a Transition Level 2 or 3 thousand feet above the Transition Altitude so that ATC do not have to worry about separation between aircraft flying at altitudes and those at flight levels unless the QNH is unusually high (oh I do hope I got tht the right way round!). I presume such States do not have traffic flow problems and can afford to lose two or three levels......but that's really another issue.

In the UK the rules are not very clear - it's a while since I looked in detail but a uick scan of the relevant docs suggests not much has changed - but if you look in the AIP ENR 1.7 para 3.3 it saysThis clearly indicates that, in the UK, Transition Level is expected to be the first 'proper' FL that exists above the Transition Altitude. It may well be that some pilots want, for some reason, to ensure that there's a certain minimum vertical distance between themselves at a FL and those who choose to fly below Transition Altitude and avoid flying at the true Transition Level. It's also a fact that some ATC units/individual controllers will only allocate a minimum FL that provides a Transition Layer of at least 1000ft (whether it's necessary for separation purposes or not) - but this is not a requirement.

DFC

Aircraft A tracking 050 FL70 ground speed 240Kt

Aircraft B is tracking 050 FL70 groundspeed 120Kt

If aircraft B is in aircraft A's 12 O'Clock then as far as aircraft A is concerned, aircraft B is approaching it from directly ahead at the same level and the closure rate is 120Kt.

When one's aircraft makes a 120Kt impact with another aircraft in cloud the fact that they impact the tail rather than the nose matters little.

The point being that the Quadrantal rule provides absolutely zero separation.

VFR flights are recomended to comply with the rule. Can can if they want ignore the rule and the recomendation.

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G-EMMA,

Well one case could be where you mis-set the DI and actually fly a compass heading of 300 for 20 minutes when you should have flown a compass heading of 330. It would be nice to be able to convert the compass heading to magnetic and then to true before using basic mental calculation to work out the track actually flown so that you can find yourself.

However, the real idea behind it is to ensure that you fully understand deviation and variation and can apply those corectly.

I agree that the question is very long winded and very much open to interpretation but it does get you thinking about the various air masses as well as localised weather features. If you will never fly whan there are showers about then on the basis that the UK has a polar maritime airflow much of the time then you are not going top fly.

Basic navigation must include the training for diversions arround showers or the planning in terms of fuel so that one has the ability to hold and wait while a shower passes through the proposed track.

Of course it is safe to be on the goround. However if you read the questions carefully and combine all the information available you will see that there is a reasonable answer.

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Spitoon,

You should have said lower! but everything else is correct.

Regards,

DFC