Questions
Thread Starter
Join Date: Jan 2006
Location: England
Age: 44
Posts: 21
Likes: 0
Received 0 Likes
on
0 Posts
Questions
Hihi
As im sure there will be people out there that have an interview lined up, and may come across questions regarding the context of the study material, I have started this thread whereby people can post questions, and kind-hearted people can help answer them
Pressure Settings
Im currently reading Air Traffic Control by Duke and I can't get my head around the following. It says that all aircrafts in the same area will be flying at the same level with synchronised altimeters. The reading given by the altimeter will only be correct when actual pressure is 1013.25; at all other pressures, the level will be more or less than the true level but whether the true setting is 1013.25 or not is irrelevant as all aircrafts are on the same setting, and any variation in actual level will be common to all.
??? Does this mean, all aircrafts, when at a certain level, set their altimeter to the pressure level of 1013.25 millibars to ensure proper separation between aircrafts?
Do we have to be as specific as this for the interview??
I apologise in advance if this is a dumb question.
Bee
As im sure there will be people out there that have an interview lined up, and may come across questions regarding the context of the study material, I have started this thread whereby people can post questions, and kind-hearted people can help answer them
Pressure Settings
Im currently reading Air Traffic Control by Duke and I can't get my head around the following. It says that all aircrafts in the same area will be flying at the same level with synchronised altimeters. The reading given by the altimeter will only be correct when actual pressure is 1013.25; at all other pressures, the level will be more or less than the true level but whether the true setting is 1013.25 or not is irrelevant as all aircrafts are on the same setting, and any variation in actual level will be common to all.
??? Does this mean, all aircrafts, when at a certain level, set their altimeter to the pressure level of 1013.25 millibars to ensure proper separation between aircrafts?
Do we have to be as specific as this for the interview??
I apologise in advance if this is a dumb question.
Bee
Combine Operations
Join Date: May 2005
Location: U.K.
Posts: 687
Likes: 0
Received 0 Likes
on
0 Posts
"Im currently reading Air Traffic Control by Duke and I can't get my head around the following. It says that all aircrafts in the same area will be flying at the same level with synchronised altimeters."
No, I can't get my head around that, either. All aircraft in the same area should normally have the same pressure set, but certainly not all flying at the same level.
"The reading given by the altimeter will only be correct when actual pressure is 1013.25; at all other pressures, the level will be more or less than the true level but whether the true setting is 1013.25 or not is irrelevant as all aircrafts are on the same setting, and any variation in actual level will be common to all."
Altimeters are designed and calibrated to operate in the International Standard Atmosphere, which does not exist anywhere on Earth. So, if an altimeter ever indicates the actual altitude, that is purely coincidental. However, because they are calibrated to the same, albeit fictitious ISA, then they should all be in error by the same amount. They should all tell the same lie, as it were.
The standard pressure setting should be used when flying above the transition altitude, and quadrantal or semicircular Flight Levels used, which are designed to give safe separation.
No, I can't get my head around that, either. All aircraft in the same area should normally have the same pressure set, but certainly not all flying at the same level.
"The reading given by the altimeter will only be correct when actual pressure is 1013.25; at all other pressures, the level will be more or less than the true level but whether the true setting is 1013.25 or not is irrelevant as all aircrafts are on the same setting, and any variation in actual level will be common to all."
Altimeters are designed and calibrated to operate in the International Standard Atmosphere, which does not exist anywhere on Earth. So, if an altimeter ever indicates the actual altitude, that is purely coincidental. However, because they are calibrated to the same, albeit fictitious ISA, then they should all be in error by the same amount. They should all tell the same lie, as it were.
The standard pressure setting should be used when flying above the transition altitude, and quadrantal or semicircular Flight Levels used, which are designed to give safe separation.
Join Date: Jun 2004
Location: Atlanta,GA
Posts: 94
Likes: 0
Received 0 Likes
on
0 Posts
hehe... I just means that everyone is flying witht their altimeters set to the same datum. That the altimeter is not always (never) showing the true altitude is accounted for by setting a transition level where pilots will transition from flying on QNE (1013.25) to the airfield QNH/QFE and therefore ensure proper altitude readouts. One ofcourse needs to take the temperature deviation from ISA into account, but its normally neglected if its not alot colder than ISA.
So when flying with 1013.25 set you are flying on a Flightlevel and when on the local QNH you are flying on an Altitude.
Got it? Im crap in explaining.
cheers /duece
So when flying with 1013.25 set you are flying on a Flightlevel and when on the local QNH you are flying on an Altitude.
Got it? Im crap in explaining.
cheers /duece
Join Date: Oct 1999
Location: Anywhere
Posts: 2,212
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by babydeb
Does this mean, all aircrafts, when at a certain level, set their altimeter to the pressure level of 1013.25 millibars to ensure proper separation between aircrafts?
Altimetry 101, I'll make it as basic as possible.
Below a pre-determined altitude (normally 3000ft in the UK, but can be higher in certain areas) Pilots will set QNH - this will give altitude relative to mean sea level and is based on actual barometric pressure in that area at sea level. Above this altitude (known as the Transition Altitude) Aircraft will set the Standard Altimeter Setting of 1013.25mbs. When this is set aircraft report their level in terms of Flight Levels (6000ft = Flight 60, 12,500ft = Flight Level 125 etc etc).
Provided all aircraft are on this setting (which is NOT known as QNE, contrary to duece 19's post - this is something totally different) then you have a common datum above the Transition Altitude by which to separate them - normally by 1000ft vertically.
Last edited by Chilli Monster; 4th Feb 2006 at 19:02.
It seems that Ive missed something vital during groundschool.Join Date: Apr 2001
Location: UK
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Chilli Monster
QNE - the level indicated on an altimeter when 1013.25mb is set. Sometimes used at mountain landing strips
i.e - QNE is 16,000ft
A common misunderstanding.
i.e - QNE is 16,000ft
A common misunderstanding.
I think!
Join Date: Apr 2001
Location: UK
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
Don't worry bee, altimetry is a bit of a black art to most people! I remember being asked the old faithful at my NATS interview (long time ago now!) of "an aircraft parks at night with a QFE of 1003, the altimeter reads 0 feet. The next morning, the altimeter reads 150 feet. What is the airfield QFE?"
Well, at least it killed 15 minutes of interview!
And I got it wrong! (Multiplied instead of dividing and got a stupid QFE figure)
And I got the job.
Well, at least it killed 15 minutes of interview!
And I got it wrong! (Multiplied instead of dividing and got a stupid QFE figure)
And I got the job.
Thread Starter
Join Date: Jan 2006
Location: England
Age: 44
Posts: 21
Likes: 0
Received 0 Likes
on
0 Posts
Ohmigawd!! Will they ask that?? I don't even know how to calculate that!!!
Would you be so kind as to explain the calculations involved for a question like that for me??
Bee
Would you be so kind as to explain the calculations involved for a question like that for me??
Bee
Join Date: Apr 2004
Location: UK
Posts: 130
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by the hunted one
Don't worry bee, altimetry is a bit of a black art to most people! I remember being asked the old faithful at my NATS interview (long time ago now!) of "an aircraft parks at night with a QFE of 1003, the altimeter reads 0 feet. The next morning, the altimeter reads 150 feet. What is the airfield QFE?"
Well, at least it killed 15 minutes of interview!
And I got it wrong! (Multiplied instead of dividing and got a stupid QFE figure)
And I got the job.
Well, at least it killed 15 minutes of interview!
And I got it wrong! (Multiplied instead of dividing and got a stupid QFE figure)
And I got the job.
150 /30 gives 5 millibars difference - so the QFE in the morning is 998 (I hope I worked that out correctly)
Last edited by TATC; 4th Feb 2006 at 20:35.
Join Date: Jun 2000
Location: UK
Posts: 683
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by the hunted one
Don't worry bee, altimetry is a bit of a black art to most people! I remember being asked the old faithful at my NATS interview (long time ago now!) of "an aircraft parks at night with a QFE of 1003, the altimeter reads 0 feet. The next morning, the altimeter reads 150 feet. What is the airfield QFE?"
With this, the Hunted One has opened a potential can of worms! There are many different ways of looking at this kind of altimetry problem and often people get confused - so before too many variations appear, you might like to try this.
Just two principles are required here - once they are understood, the answer is simple.
1 The relationship between height (feet) and pressure (millibars) is that (at sea level) 1 millibar equates to 27 feet - this is often rounded to 30 feet for simplicity. [Incidentally, as height increases the number of feet corresponding to a millibar increases steadily.]
2 As you know, the altimeter has a subscale indicating millibars which is adjusted to the setting required - i.e standard (1013.25) QNH or QFE, etc - and with an aircraft on the ground or in level flight, as you change the subscale setting, the altimeter reading will change accordingly. The important thing to remember here is that both change in the same direction - i.e. if you INCREASE the millibar subscale, the indicated altitude will also INCREASE.
Taking these two together, it should be clear that, if the altimeter is reading 150 feet on the ground, to reduce it to zero (i.e. to set it to QFE) you need to "wind off" (150 / 30) = 5 millibars. Thus, in the question above, the next morning's QFE is (1003 - 5) or 998 mb. Easy!
Hope this helps with the understanding!
Join Date: Apr 2001
Location: UK
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by TATC
You should have divided anyway-
150 /30 gives 5 millibars difference - so the QFE in the morning is 998 (I hope I worked that out correctly)
150 /30 gives 5 millibars difference - so the QFE in the morning is 998 (I hope I worked that out correctly)
They also showed me maps of different airfields and asked me to show them strengths and weaknesses of each airfield layout.
They also asked me about the differences between Primary and Secondary radar and the strengths and weaknesses of each.
And they gave me a scenario of different aircraft arriving at a hold, who would you make number 1, 2, 3 and 4 between a B747, a hercules, a Cessna and a helicopter or whatever.
The only other one I remember is the old trick question of where they give you a set of 4 aircraft with ETA's and ask what order they will arrive at the hold. Don't fall into the old speed trick. The estimates is the clue. Doesn't matter how slow an aircraft is, if it is 5 minutes away, it will get there before a swept-wing tornado that is 6 minutes away. It may sound obvious, but you would be amazed at how many people will say that the Tornado will get there first!
That's all the questions I remember now (apart from asking me what newspaper I read) and some topical stuff from the time about London City Airport and recommendations about flame retardent materials in aircraft cabins and passenger smokehoods, which never got adopted. To cover yourself for these type of questions, buy Flight International and another couple of aviation mags (I used Aircraft Illustrated at the time) in the run-up to your interview, that way you will know what the current "hot topic" is likely to be.
Still, not a bad memory considering my interview was in 1988!
Join Date: Jan 2006
Location: Swanwick
Age: 44
Posts: 33
Likes: 0
Received 0 Likes
on
0 Posts
Babydeb..... don't worry. They wouldn't be so mean as to ask you anything as complex as that!! I hope.
Questions such as, "Do you know how an aircraft manages to navigate?" and "What different types of Air Traffic Control are there?" were about as complex as my questions got. Hopefully they'll be the same for you
Questions such as, "Do you know how an aircraft manages to navigate?" and "What different types of Air Traffic Control are there?" were about as complex as my questions got. Hopefully they'll be the same for you