VOR, DME and ILS

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• Physics
• Higher Education (non-degree)

VOR, DME and ILS

Learning goal

I can explain what VOR, DME and ILS tell a pilot, and why using more than one navigation source is useful.

What helps a pilot navigate when the ground cannot be seen?

Use this to surface prior ideas such as instruments, radio signals, maps, GPS, runway guidance or cross-checking. Accept broad associations at this stage.

How aircraft navigate

• Pilots do not rely only on seeing the ground

• Radio navigation aids send usable signals to the aircraft

• Different systems give different kinds of information

• Together, they help pilots know position and approach path

This opens the lesson from a familiar idea: flying without outside visual reference. Keep it general before naming systems.

Three main systems

• VOR gives angular or bearing information

• DME gives distance information

• ILS gives guidance for landing approach

• Each system supports a different part of navigation

VOR: what the name means

• VHF = Very High Frequency

• Omnidirectional = signal can be used in every direction around the station

• Range = a navigation aid covering an area around the station

• VOR is a ground-based radio navigation aid

Keep the emphasis on meaning, not memorising every word in isolation. 'Omnidirectional' matters because the station works all around itself.

VOR gives angular position

• The aircraft compares the received signal with the station reference

• This shows its angular position relative to the station

• The information is about direction from the station, not distance

Meet the radial

• A radial is a direction extending outward from a VOR station

• Radials are measured in degrees

• An aircraft directly north of the station is on the 360° radial

• The station is the centre point for every radial

A common confusion is mixing up heading and radial. A radial is named by the direction from the station outward.

Reading a VOR indicator

If the desired course shows to the right, the aircraft is left of the desired course. The indicator tells the pilot where the selected course lies relative to the aircraft's present position.

This is the key interpretation point from the indicator slide. Keep the wording consistent: desired course right = aircraft left of course.

An aircraft directly north of a VOR station is on which radial?

A

180°

B

360°

C

090°

D

270°

Tests the key idea that radials are named by direction outward from the station, not by aircraft heading.

VOR essentials

A VOR is a ground-based radio navigation aid. It gives angular information about an aircraft's position relative to the station. A direction extending outward from the station is called a radial. If the desired course shows to the right, the aircraft is left of the desired course.

angular

radial

left

distance

localiser

right

glideslope

All three blanks come from slides 4 to 7: angular information, radial, and indicator interpretation.

DME: distance only

• DME stands for Distance Measuring Equipment

• It tells the pilot how far the aircraft is from the DME station

• Unlike VOR, it does not give angular or bearing information

VOR and DME compared

• VOR → angular or bearing information

• DME → distance information

• VOR helps show direction relative to a station

• DME helps show range from a station

The navigation pair

Using VOR with DME gives two pieces of information at once:

• direction from the station

• distance from the station

Together, these help a pilot work out the aircraft's position much more clearly than either system alone.

If only DME were available, the pilot would know how far away the aircraft was, but not which direction from the station.

Why are VOR and DME more useful together than alone?

Expected elements: VOR gives direction from the station; DME gives distance from the station; together they help a pilot fix position more clearly; with only DME, direction would be missing.

If an aircraft has only DME, what information is missing?

A

Runway lighting

B

Vertical path

C

Direction

D

Radio frequency

Targets the contrast built across slides 8 to 10: DME gives distance only, so direction from the station is missing.

ILS: guidance for approach

• ILS stands for Instrument Landing System

• It is used during an approach to a runway

• It gives guidance to help the aircraft stay correctly lined up

The two parts of ILS

• Localiser → lateral guidance

• Glideslope → vertical guidance

• Lateral means left and right

• Vertical means up and down on the approach path

Use the exact labels localiser and glideslope consistently. Students often remember them better as left/right and up/down.

Localiser

• The localiser provides lateral guidance relative to the runway centreline

• It helps the aircraft align with the centreline during approach

• Left of centreline, right of centreline, or aligned are all localiser positions

Glideslope

• The glideslope provides vertical guidance for the approach path

• It helps the pilot control whether the aircraft is above, below, or on the correct descent path

• It does not give heading or distance

Building the ILS picture

Localiser → lateral guidance

Glideslope → vertical guidance

Pilot or flight system interprets both → aircraft remains aligned with the desired approach path

This slide summarises the whole ILS mechanism without adding extra technical detail.

Interpreting approach information

• Localiser shows desired course left → aircraft is right of centreline

• Glideslope shows above → aircraft is above the desired path

• DME gives the aircraft's distance from the station

• Each display gives one part of the full navigation picture

Keep the indicator logic explicit. Students must separate aircraft position from where the desired path appears on the instrument.

One aircraft, three systems

• VOR → angular or bearing information

• DME → distance

• Localiser → lateral runway alignment

• Glideslope → vertical approach guidance

Which part of the ILS gives vertical guidance?

A

Glideslope

B

Radial

C

Localiser

D

DME

Checks the load-bearing distinction localiser = lateral, glideslope = vertical.

Build the ILS picture

ILS is used during an approach to a runway. The localiser gives lateral guidance, while the glideslope gives vertical guidance. Together, they help the aircraft stay on the desired approach path.

localiser

glideslope

approach path

VOR

distance

centreline

radial

Echoes slides 11 to 17 and reinforces the full ILS picture rather than isolated terms.

How do localiser, glideslope and DME complete one picture?

Expected elements: localiser left means desired course is left, so aircraft is right of centreline; glideslope above means aircraft is above desired path; DME gives distance from the station; each display shows one part of the picture.

Navigation information is not perfect

Ground-based navigation aids can become unreliable. Pilots should not assume the indication is always correct, because signal interference, equipment problems, terrain effects or coverage limits can affect what is received.

This is the conceptual shift into limitations and resilience. Emphasise checking, not mistrusting everything.

Types of limitation

• Coverage: signal is not available everywhere

• Signal interference: the received information may be disturbed

• Equipment failure: aircraft or ground equipment may not work correctly

• Terrain or obstructions: mountains or obstacles can affect reception

• Aircraft equipment requirements: the aircraft must carry suitable receiving equipment

Example: mountainous terrain

• Unreliable indications near mountains may point to terrain effects

• Equipment failure could still be another possible cause

• Pilots consider more than one explanation before trusting the information

This mirrors the fault-investigation scenario. The main idea is diagnostic thinking: more than one cause can produce unreliable indications.

Choosing the right aid

• Need angular or bearing information → VOR

• Need distance information → DME

• Need lateral runway approach guidance → ILS localiser

• Need vertical approach guidance → ILS glideslope

• More than one system can be useful at the same time

Near mountains, what should a pilot investigate first?

A

Terrain effects

B

Tailwind only

C

Cloud height

D

Runway length

Based on the mountainous terrain example. The distractors are nearby aviation ideas but not the limitation discussed here.

Which limitation seems hardest to spot quickly in flight?

1

Coverage limits

2

Signal interference

3

Equipment failure

4

Terrain effects

Why use more than one navigation source?

Expected elements: different systems provide different information; pilots can cross-check one source against another; if one becomes limited or unreliable, another may still help; this improves resilience.

Exam-style answer: VOR

• VOR stands for VHF Omnidirectional Range

• It is a ground-based radio navigation aid

• It provides angular information about the aircraft's position relative to the station

Useful for both the 1-mark acronym question and the 2-mark function question.

Exam-style answer: DME

• DME provides distance information

• It tells the aircraft how far it is from the DME station

• Unlike VOR, it does not provide angular or bearing information

Exam-style answer: Localiser

• The localiser is part of the ILS

• Its purpose is to give lateral guidance

• It helps the aircraft align with the runway centreline during approach

Exam-style answer: Glideslope

• The glideslope is part of the ILS

• Its purpose is to give vertical guidance

• It helps the aircraft stay on the correct approach path

Why use more than one source?

Pilots may use more than one navigation source because different systems provide different information. Using several sources allows cross-checking and gives greater reliability if one source becomes limited or unreliable.

This captures the full 3-mark idea: different information, cross-checking, resilience.

Traditional and modern navigation

• Modern aircraft may also use satellite navigation or GNSS

• Ground-based aids and satellite systems can support each other

• Different sources improve cross-checking, availability and resilience

• Conventional aids remain useful if another system has limits

Do not over-expand into GNSS theory; keep it as an extension about complementary sources.

The full approach picture

• Angular or bearing information → VOR

• Distance from the station → DME

• Lateral runway alignment → localiser

• Vertical approach guidance → glideslope

• Multiple systems give a fuller and more reliable picture

This functions as the final synthesis before the glossary.

Which system gives angular or bearing information?

A

ILS

B

DME

C

VOR

D

Glideslope

A compact exam-style recall check from the summary and exam-answer slides.

Full approach summary

For the full approach picture, VOR gives angular information and DME gives distance from the station. On an ILS, the localiser gives lateral runway alignment and the glideslope gives vertical approach guidance.

VOR

DME

glideslope

ILS

radial

coverage

interference

This mirrors the final synthesis slide and prepares students for written recall.

What is one thing you will remember from today's lesson?

Which part felt hardest: VOR, DME or ILS?

How confident do you feel explaining VOR, DME and ILS now?

Glossary

VOR - VHF Omnidirectional Range, a ground-based radio navigation aid that gives angular information relative to a station

DME - Distance Measuring Equipment, a system that tells the aircraft its distance from a station

ILS - Instrument Landing System, a system that provides guidance during an approach to a runway

Localiser - The part of the ILS that gives lateral guidance relative to the runway centreline

Glideslope - The part of the ILS that gives vertical guidance for the approach path

Radial - A direction extending outward from a VOR station, measured in degrees

Navigation aid - A system that helps pilots determine position or guidance