ILS question
 

If you are 15 miles out on glide slope with a 3 degree angle, how high are you agl? Does anyone have a good quick rule of thumb for this?

p.s while im here, if a brand new engine is at 1.8 epr and producing 60,600 lbs of thrust, ten years later will it still produce the same thrust for 1.8?

thanks in advance for any inputs,
D

A good rule of thumb is 3 times your height.

Therefore at 15 miles on a 3 degree slope you should be at 5000feet.

Also a rule of thumb for working out what your vertical speed should be on a 3 degree slope is 5 times your groundspeed. ie. 150kts x 5 750 feet per minute.

:ok:

3 x your distance is a bit closer I think (not to mention being easier to work out when you want to know how high you should be at a specific distance.) So at 15 miles you want to be 4,500'.

Another good way of working out your ROD is dividing your GS by 2 and adding a 0 at the end of your answer.

ie, GS of 160/2 = 80 + 0 = 800 feet a min,
GS of 150/2 = 75 + 0 = 750 feet a min,
GS of 140/2 = 70 + 0 = 700 feet a min

GS of 136/2 = 68 + 0 + 680 feet a min and so on.

Seems to work and gives the same answer as the GS x 5 rule. Depends on how good your mental arithmatic is I suppose.

However, these rules of thumb will generate a number for height above airport elevation, which may differ wildly from AGL where you're at, 15 miles from the airport.

Just a paranoid ATC putting his two cents in...

Dave

Are you ever "ON" the glideslope at 15 miles?

As to the EPR question...simple answer yes! The EGT will go higher as the engine gets older but the thrust will be exactly the same assuming of course that the EPR measuring systems are OK. This is one of the benefits of an EPR system as opposed to just measuring N1 I am told.

AerocatS2A answer is correct.

On a 3° GS you'll lose about 300' per NM. So when you are 15 NM out on GS you should be at 4500' above airport elevation (or rather threshold elevation).

Generally, to find the number of feet per NM descent, multiply the descent angle by 100. So with a 3° angle you will get 3x100 = 300'/NM. That leads us to 4500' at 15NM out on GS.

With a 2.5° angle: 2.5x100 = 250'/NM. At 15NM out on GS you should be at about 3750' above threshold elevation.

Hi everyone, I was reading a book on IFR and ILS approaches and came across the term Lobes'. The book was a little vague on what a 'Lobe' does except to say it had somehting to do with the glidepath :confused: . If anyone could should some light on the matter it would be appreciated.

Newbie1

ILS Lobes
 

Quick Google search "ILS systems lobes" yielded many results, this link goes to a technical document but show, digramatically the lobe concept.
http://www.pn.ewi.tudelft.nl/educati...2/notes/h7.pdf

Cross Checks.
 

A 3 degree glide slope gives a change of 320ft in height for every 1NM. Therefore at 10NM from the Rwy. Your altimeter should read 3200 ft AGL. If the elevation of the runway is 200 ft then the altimeter will read 3400ft, because the altimeter is reading height above Mean Sea Level.

Newbie1.

Lobes are those funny looking things that looks like a stretched bannana on any LLZ, GS diagram. If you can get hold of the Oxford Air Training Radio Aids book it explains all the aspects of the construction and use of the ILS.

shgsaint:
By dividing by 2 then multiplying by 10 you are just multiplying by 5. You haven't discovered some amazing new aviation rule of thumb, just learnt an easier way to do maths that most of us figured out at primary school!

Sorry there Fournicator. Never said I discovered it. Should of said it was what I was told but there you go. Getting shot down when you try to help someone. :rolleyes:

I don't appreciate the last remark. KISS (Keep It Simple Stupid)

The ILS G/S isn't generally calibrated above 3000 ft aal so no guarantees at 15 miles.

BTW Brown eyes, Altimeters read above the datum set by the pilot when I last looked.:ok:

Sorry if I hurt your feelings.

issi noho
 

Well obviously the altimeter reads above the datum set, but when one is flying an ILS the pressure altimeter is normally set to the aerodrome QNH unless one is flying in the military or as I read in Russia where they use QFE. Thats what I was getting at.

Geneva RW23 has GS intercept at about 7000', about 2000' AAL - 17nm out if I remember correctly.

No worries.

I'll be the first to admit my maths is a little rusty. But then not being a professional pilot it doesn't need to be sharp.

Just my preferred way of remembering/working out the ROD on an ILS.

And don't it make your brown eyes blue....

Fairy nuff

..............................
 

325 feet * 15 miles

Discussing that safety film about the G/S problem a few days ago, ‘lobes' popped into my mind after........er, 40 years. Must have come from my frontal lobes.

The thing is, as I said there, it would be a very steep slope on a secondary lobe, the sort of approach that we used to do in DC3s :E