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boeing320
7th Oct 2008, 14:09
hello. i have some questions about the way approaches are labelled on plates. i searched but no joy here or wikipedia!

is there any differece between a 'Locator' approach and an 'NDB' approach? is it to do with the power output of the NDB perhaps?

also, why do you see one approach called a VOR approach and another called a VOR DME approach, when both have DME distances associated? it makes sense to call it 'VOR' or 'NDB' if its a timed approach and theres no DME, but thats not always the case, sometimes there is)

at the end of the day, you just do what it says on the plate! but i wondered if theres some technical difference i'm not aware of.

cheers!

411A
7th Oct 2008, 14:29
First off, you might spell correctly...it is Jeppesen.

Locator vs NDB.

If the approach is based upon a compass locator, it will be labeled as such.
IE: Locator.

VOR and or VOR/DME.

Example.
Normally, a VOR/DME approach would be flown.
However, if for some reason the DME portion were unserviceable, the approach could still be flown, generally to higher minimums.
Several other variations.

eyeinthesky
7th Oct 2008, 15:10
For the perfectionists such as 411A (as shown by the 'spelling' quip):

"generally to higher minimums"

should be:

"generally to higher minima":p

Back to the question:

It is my understanding that a Locator is of a lower power output than an NDB. Is it also the case that a Locator is usually positioned somewhere on the approach to one of the runways, whereas and NDB will not necessarily be so? A locator therefore gives a positive check of position with no further aids required as you overfly it, whereas distance to/from an NDB or MAP can only be calculated by use of a DME, co-located or not, or through timings.

SNS3Guppy
7th Oct 2008, 17:40
Is it also the case that a Locator is usually positioned somewhere on the approach to one of the runways, whereas and NDB will not necessarily be so? A locator therefore gives a positive check of position with no further aids required as you overfly it, whereas distance to/from an NDB or MAP can only be calculated by use of a DME, co-located or not, or through timings.


By definition, if a NDB is located somewhere on the approach to a runway, if one is flying an NDB approach. Think about it.

Distance to and from an NDB is most often predicated on timing...not DME.

SFI145
7th Oct 2008, 18:25
How on earth do the above three posts help the original poster?
In particular 411A's unhelpful scolding of the poster adds nothing. Why don't we all hold back until we have a useful answer to the original post?

fullyspooled
11th Oct 2008, 12:38
Addressing the question in point:

A Locator Approach is one where the primary aid is a compass locator, which as you correctly point out has a significantly lower power output. The Locator will always be situated on the extended centreline of the landing runway, at approximately four miles.

Similarly, an NDB Approach is flown using the primary aid of an NDB, although the NDB may be positioned either on the airfield, or at either end of the landing runway extended centreline..

Regarding your second query, an NDB/DME approach is an approach that is designed to be flown using both the NDB and the DME. If the DME is not available you may not fly the approach, but may instead be able to fly an alternative NDB approach - which will be of a different profile, and will usually be subject to increased minima.

I hope I have not misled you, but stand to be corrected.

The Real Slim Shady
11th Oct 2008, 13:02
The Jepp chart training CD recognises VOR, NDB, LOC,GPS and LDA approaches as non precision.

The DME element is regarded as an extra and will be specified, although the "raw" apporach using timing is still valid but to higher minima.

The NDB may be a locator or an ndb: the LOC is the localizer element of an ILS installation the LDA is a displaced localiser approach i.e offset by up to 15 degrees.

fullyspooled
12th Oct 2008, 18:24
Slim, you quite correctly define the non precision approaches, but an NDB approach is indeed different from a "Locator" Approach. The latter is entirely different again from a "Localiser" approach.

A "Locator"Approach is one based on the primary aid of a Compass Locator, and has nothing to do with the lateral guidance provided a stand alone Localiser, or the Localiser portion of an ILS.

Perhaps I miss read your post, but just wanted to clarify in case there was confusion.

The Real Slim Shady
12th Oct 2008, 19:13
Fullyspooled, a locator is simply a low powered non directional beacon and hence an NDB approach or LCTR approach are effectively the same.

The FAA has some guidance on the nomenclature:

Compass Locators. The general term "compass locator" also covers NDB/OM, LMM, and LOM regardless of output power or type. The term is applied only to a non-direction radio facility which is located at the VHF middle or outer marker site (front course) of an ILS. It is assigned a name-code and a two-letter identifier. The two-letter identifier is derived in the following manner:

(a) The three-letter localizer identifier is considered as a base.

(b) The first and second letters of the three-letter localizer identifier are assigned to the outer marker compass locator (LOM) and the second and third letters are assigned to the middle marker compass locator (LMM).


and further on LDA approaches:

Localizer Type Directional Aids (LDA). This equipment is of comparable accuracy to an ILS localizer and may be used in conjunction with a glide slope and/or markers. It usually does not meet ILS siting standards and is not part of an ILS. It is, however, assigned a three-letter identifier preceded by the letter "I"

Finally on NDBs:

Non-directional Radio beacon. Non-directional radio beacons are assigned three-letter identifiers except when they are also the outer compass locator (LOM) or middle compass locator (LMM) of an ILS, or placed at a marker site of an ILS. See Compass Locators above. The same basic three-letter identifier cannot be shared by a terminal NDB and an ILS at the same location.

What's in a name, huh??

boeing320
13th Oct 2008, 16:09
thanks for your input everyone.

So, for an NDB approach, its a higher powered navaid either on the field or not on the field (can be positioned more or less anywhere, around 4nms ish or further out)

Whereas a locator approach = lower powered NDB beacon (seems it can be anywhere between 10nms and very short finals, from what i've seen).