So .. 71 and that is answer (a+c)/2 ? :p

Well I think 079, but I'm open to comments

Just got that exact question in AvExam

76 was their answer

Or.. if you're on a transoceanic flight you'll most probably have a computer able to that computation for you :p

and what was their explanation?

How the are we supposed to guess if they're talking about wake turbulence category or approach category ?
https://gyazo.com/26a4609ce71ad40482b07a94aed9ca46
https://i.gyazo.com/e06e9a296a75cb43...9046dbe357.png

It resembles the one I had however everybody will use some variation of that to get the right answer
https://i.gyazo.com/526f9f0281c28855...5c004ee547.png

ah their earth rate is different to mine, 19 deg rather than 13 deg. I copied Paco for that figure - I'll check it.

.... not multiplied by 1.5...

earth rate is 19.5 deg, amended total drift is 19.5 + 8.7 = 28.2

and whether you apply it to the great circle or rhumb line tracks the average is 076. Agreed.

I really shouldn't attempt these calculations!

And now that I have finished comms, ops, air law and half of instruments questions on avexam, I do realise that it is actually possible to learn the answers to the questions.

I could not believe that one could remember thousands of pieces of data, but even I with a rather bad memory, the answers that can't be figured out by understanding and thinking can very well pop up in my mind because I just remember having seen them.

Which is a bit frightening.... as well as satisfactory because, you know, I have to pass my exams in a short time :p

"I really shouldn't attempt these calculations!"

Neither should I :) Back to sleep....

What is even more embarrassing is that the question has been in our database since 2011, and I didn't look.

LOL!! I wonder if it is still in the real one? Maybe I will ask!

I need your help on the following questions-sentences.
Please,correct me if I am wrong!


1)The two points are on the same parallel of latitude (60o).The part of parallel of latitude that connects them is a rhumb line since it cross the meridian of 10 and 20 degrees of longitude at the same angle (which is 90 degrees).
Do you agree?

2)An aircraft that will fly from A to B (eastward direction),will have a constant TRUE TRACK of 90.


3)The gyro compass is aligned on the point A with TRUE north.So,when the trip starts the gyro compass shall indicate 090 (since there is no wind,right).But as the aircraft flies due to precession the indication of gyro compass is altered.
Do you agree?

4)In order to fly on a constast gyro track we have to alter the TRUE HEADING in the beginning of the trip by the half of the precessions?


Thanks for your time!

1) yes
2) No. A true (and complete) statement would be "An aircraft can follow the rhumb line track A to B, in which case its true track would be a constant 090 deg, but the path will be curved. It can also take the shortest straight line route, a great circle, in which case the intitial true track will be less than 090, its final true track greater. The aircraft could also take any number of curved tracks other than the rhumb line between A and B."
3) See above. This is correct assuming you try to follow a rhumb line path, but why would you?
4) Will think about this. It is probably true, but your true heading will represent neither the rhumb line nor great circle track. The aircraft will follow a curved path to the north of the great circle.

I do not believe that the above will always be the case.

At the Equator there will be no ER or TW, so you will flt along the Equator.

When going west in the northern hemisphere at a ground speed equal to the rotational speed of the Earth at that latitude, the TW will be equal and opposite to the ER, so there will be no wander. This means that you will fly along the parallel of latitude on a 270 true heading.

If you fly west at any higher ground speed the TW will be greater than the ER, so your track will be south of the Parallel of latitude.

I could be wrong of course.....this age-induced brain fade is a terribly sneaky creature!

You are right, Keith. Depending on hemisphere and direction of travel the constant gyro track could be north or south of the great circle. I only meant that, in this case, it ran to the north.

https://i.gyazo.com/a2658fc2c278618a...16ebb829d0.png
Doesn't it rather depend on the latitude for which the compass was made ?

By the way, suppose I buy a compass for 45N and go use it at 45S : won't it be totally upset and not horizontal ?
How can you have a compass fit to use from -45S to 60N, an amplitude which many long haul aircraft have ? (I know they have real means of measuring heading, but there must be an is a standby/emergency compass in these aircraft as well)

Thanks

It does, there are compasses made specific to hemisphere but I have only been able to find references to 'orienteering' style compasses. I concluded that aircraft compasses are not compensated for hemisphere but cannot actually confirm that, its just not mentioned anywhere I can find. It makes sense, though.

This is an example of a question which requires the candidate to do a little bit of deductive work to understand what the author was really asking. The question does not actually say that the compass has been set for any particular latitude, so it is probably best to start by ignoring this possibility. In this case Option A is correct.

If however the compass had been set for some latitude other than zero, then as we move away from the Equator, we would expect the errors to decrease until we reached the latitude for which the compass had been set. The errors would then increase gradually as we moved beyond that latitude. In this case the correct option would be “Decrease then increases”. This is not an option, so we can reasonably deduce that the author of the question did not intend us to employ that interpretation.


This subject was discussed in a thread in the PPL Forum some time ago, and the discussion included how compasses are balanced for different latitudes. Some contributors argued that aircraft compasses are not balanced in this way, but an aircraft compass manufacturer provided the following statement:


The thread becomes rather long and dreary, with much argument about what PPL students should and should not learn, but for those who wish to read it the link is:


http://www.pprune.org/private-flying...ht=blob+solder

I suggest we just forget about the usefulness of this question in any serious flying context.. I've flown once with a directional gyro failure. At this time, I had no idea about compass errors but that did not stop me from navigating precisely with it.

I thought that the error was linked to the mass (compensating the dip) lagging behind the axis, isn't it?
I read your post in the linked topic, and you raised a good point : if there was no dip compensating mass, but just a mass well below the C of G, then you're right, the compass will have an "attitude angle" and dip towards the pole, hence the C of G will no longer be on the axis, hence turning/acceleration errors.

However with a non dip compensated compass, these errors should be inferior to those of a dip compensated one ? (this is suggested by Gil Stone's post but rephrased)

And finally Gil Stone tells us that some compasses will use both solutions : pendular design + a supplementary small weight to optimize the compass for a certain latitude ?

Related pic, for the lolz (it is simulation because I could not find it in a real environment)
Emergency/standby compass of an A320
http://www.flightsimlabs.com/index.p...eries-a320-3/#

Without any form of dip compensation the compass will suffer the full effects of the dipped lines of magnetic force. This will reduce the accuracy of the compass and further reduce the range of latitudes throughout which the compass would be usable.

Adding the pendulous suspension system will reduce the dipping effect thereby improving both accuracy and usable range of latitudes. But because the dipping is not completely eliminated, the pendulous suspension system introduces the turning and acceleration errors.

Adding a balance weight which is appropriate for a given latitude will eliminate the dipping completely, provided the aircraft remains at the latitude. This will also further reduce the acceleration and turning errors. If the aircraft is moved from that latitude some (reduced) degree of dipping will occur and this in turn will increase the acceleration and turning errors.

So it could be argued that by adding pendulous suspension and balance weights, the compass will achieve the best compromise between accuracy, usable latitude range, acceleration errors and turning errors.