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AAS 1 > Distance Measuring Equipment (DME) > Flashcards

Distance Measuring Equipment (DME) Flashcards

1
Q

VOR’s, NDB’s, and localizers guide the aircraft along a course; However they do not give what?

A

do not give the flight crew a fix of their actual position because the aids do not provide a distance to the station

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2
Q

What does DME stand for?

A

Distance Measuring Equipment

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3
Q

DME lowers pilot workload in having to:

A

plot and reckon position

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4
Q

Federal regulations require DME for aircraft operating at or above:

A

24,000ft (FL240)

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5
Q

What does a DME send to a ground station?

A

an interrogating pulse

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6
Q

What happens once the DME has interrogated the ground station and received a reply?

A

The aircraft DME equipment measures the elapsed time to compute the distance to the station

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7
Q

How long does it take for a DME signal to travel one nautical mile?

A

just over 6 micro seconds

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8
Q

The ground station can be one of 3 different station:

A

VOR station with DME
a TACAN station
VORTAC

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9
Q

What is TACAN?

A

Tactical Navigation developer by the military

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10
Q

What are known as VORTAC sights?

A

VOR sites that also have TACAN capability

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11
Q

DME can also be a part of what system?

A

ILS
and is listed as an ILS/DME

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12
Q

VOR with DME is known as:

A

VORDME

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13
Q

DME operates in what band?

A

UHF

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14
Q

When a VORDME or TACAN station is tuned onto the VHF nav, it is paired with?

A

the UHF frequency

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15
Q

What are the two modes of DME frequency band use?

A

X Mode and Y Mode

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16
Q

What is X Mode?

A

the old system and divided the bandwidth into channels with 0 in the 50kHz

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17
Q

What is Y Mode?

A

newer system and divides the bandwidth into channels with a 5 in the 50 kHz position

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18
Q

The X/Y system allowed for how many available channels?

A

200

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19
Q

Unlike most radar systems, DME is an active system. This means that what?

A

The system in the aircraft transmits

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20
Q

What is the calculated time it takes a radio wave to travel one nautical mile?

A

6.18 micro seconds

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21
Q

What is RRTNM?

A

Radar Round Trip Nautical Mile
12.36 micro seconds
(the time it takes for a radio wave to travel one NM and back)

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22
Q

What does the DME transponder transmit?

A

random Gaussian pairs of pulses in its assigned DME channel

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23
Q

All DME pulses are how wide at the 50% point?

A

3.5 microseconds wide
Have a rise time of 1 microsecond

24
Q

How far apart are X Mode station transmission pulses?

A

12 micro seconds apart

25
Q

How far apart are Y Mode station transmission pulses?

A

30 micro seconds apart

26
Q

DME transponders receive at a frequency different from what?

A

the frequency at which they transmit

27
Q

What kind of system is DME?
(In terms of components, not distance measuring)

A

Duplex System

28
Q

The ground station continuously sends random pulses known as:

A

Squitter Pulses or the Squitter

29
Q

At regular intervals, the transponder stops sending the squitter and instead sends out pulse pairs at a constant rate resembling dots and dashes.
The aircraft DME uses the pulse pairs to create what?

A

a 1,350Hz identification tone

30
Q

Even though the time between pulse pairs is constant, the time between pairs of pulses varies at random. This is known as:

A

Jitter

31
Q

Jitter allows:

A

a DME to recognize transponder replies directed to it

32
Q

The transponder receives the pulse pairs, delays them for either 50 or 56 micro seconds, depending on what?

A

If it is X or Y Mode
It then retransmits the pulse pair

33
Q

The time delay allows the electronics equipment to operate and for the aircraft to:

A

lock on to the station when close by

34
Q

When the DME receives the pulses back, it will lock on and:

A

remove any fault flags from the display and provide displayed distance to the station

35
Q

Once locked on, the DME starts to track what?

A

the changes in timing as the pulses return to the aircraft

36
Q

The DME calculates the rate at which the distance is changing and then begins to display:

A

other info such as speed and estimated time enroute

37
Q

The order of operation for the DME is always:

A

listen, search, lock, and track

38
Q

There are 2 additional operational modes for the DME:

A

Memory Mode and DME hold

39
Q

What is Memory Mode?

A

allows the DME to continue to display distance, speed, and ETE for a short period after a loss of signal

40
Q

Memory Mode prevents what?

A

a restart when the signal is temporarily lost due to signal blockage during aircraft maneuvers or landing gear operation

41
Q

What is DME hold?

A

locks the DME on the current frequency

42
Q

What is the heart of the DME system?

A

the processor

43
Q

What does the processor do?

A

detects and validates incoming pulses and controls the timing of the transmitter and receiver sections

44
Q

DME measures what range?

A

Slant Range

45
Q

With DME, the modulator works how?

A

like a trigger to fire off the Gaussian shaped pulses

46
Q

Light aircraft will typically use a configuration in which:

A

the control head, transceiver, and indicator are all in one panel mounted unit

47
Q

What type of antenna is the DME antenna and where is it mounted?

A

Marconi and mounted on the lower fuselage of the aircraft

48
Q

What are the two types of DME antenna designs available:

A

A small whip antenna with a ball on the end
and
a rigid blade style that is about two inches long

49
Q

Most of the generators used require the technician to:

A

set the specific antenna distance and height

50
Q

Checking the sensitivity verifies what?

A

that it locks on at low signal level

51
Q

The test for minimum lock on should be performed on:

A

more than one frequency in both X and Y Modes

52
Q

Where can the transmitter power can be read?

A

The peak transmitter power can be read from the test unit

53
Q

What does PRR stand for?

A

Pulse Repetition Rate
May sometimes also be called Pulse Repetition Frequency (PRF)

54
Q

The PRR should be checked in both:

A

search and track modes

55
Q

The distance, speed, and time to station values should agree with:

A

the test box within the limits of the maintenance manual

56
Q

Frequency is read from the test set and again should be within the limits of:

A

the maintenance manual

AAS 1 (25 decks)

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