Distance Measuring Equipment

Question 1

State the DME range in nautical miles formula

Answer 1

DME range in NM = 0.162nm/microsecond x (T - 50/56) / 2

Question 2

What does the V refer to in the DME formula?

Answer 2

V is the speed of propagation, which is 0.162 nm per micro-second.

Question 3

What does the T refer to in the DME formula?

Answer 3

T is the time in microseconds between transmission of interrogation and the reception of reply

Question 4

What does the 50 refer to in the DME formula?

Answer 4

50 is the fixed delay at the DME in microseconds( For Y channel use 56)

Question 5

Fill in the blanks:

Whilst in the _____ mode the interrogator transmits at a rate as high as ___ pps in order to “lock on” as quickly as possible. If “lock on” is not achieved after 15 000 pairs of pulses have been transmitted (100 seconds) the PRF reduces to __ pps until lock on is successful, at which point the PRF is reduced further to between __ and __ pps.

Answer 5

Whilst in the search mode the interrogator transmits at a rate as high as 150 pps in order to “lock on” as quickly as possible. If “lock on” is not achieved after 15 000 pairs of pulses have been transmitted (100 seconds) the PRF reduces to 60 pps until lock on is successful, at which point the PRF is reduced further to between 25 and 30 pps.

Question 6

Which system resides in the aircraft?

Answer 6

The interrogator

Question 7

What is the DME pair of pulses limit, and aircraft limit and what would occur if the limit is reached?

Answer 7

DME is limited to 27 000 pairs of pulses, which equates to 100 aircraft. If that limit is reached, the aircraft at greatest range will be excluded.

Question 8

What frequencies does DME use?

Answer 8

DME operates in the UHF band between 962 mhz and 1231 mhz

Question 9

Define the term DME/VOR

Answer 9

A vOR co-located with a DME

Question 10

Define the term TACAN

Answer 10

The military version of VOR/DME. Civil airborne equipment cannot obtain bearings from TACAN, only DME ranges.

Question 11

Define the term VORTAC

Answer 11

A VOR co-located with TACAN (DME ranges). A combined facility that allows a civilian aircraft to obtain VOR bearings and TACAN DME distances

Question 12

Define the term co-located VOR/DME

Answer 12

Aerials less than 100 feet apart, same IDENT.

Question 13

Define the term associated VOR/DME

Answer 13

Aerials between 100 and 2000 feet apart, same IDENT.

Question 14

The DME range formula for ground range

Answer 14

Ground range squared = slant range squared - aircraft alt in nm squared

Question 15

The DME range formula for slant range

Answer 15

slant range squared = height squared + ground range squared

Question 16

What would be the distance if directly above a DME?

Answer 16

The vertical distance

Question 17

An aircraft DME receiver rejects pulses meant for other aircraft because?

Answer 17

The random PRF is unique to each aircraft

Question 18

The aircraft DME transmitter on auto-standby will be activated when:

Answer 18

Random filler pulses of the DME ground transmitter are received by the aircraft

Question 19

What is the ground transmitter and receiver called?

Answer 19

The transponder