Chapter 5 DME Flashcards
What is DME a type of?
Secondary radar system (SSR)
What distance does DME give?
Slant range in nautical miles
How does DME calculate the range?
Based on time taken for signals to travel between the interrogator (airbourne) and transponder (ground based)
Describe the signals sent out by the aircraft to DME?
Jittered pulse pairs
How much is the delay between interrogation and response?
50 micro seconds
What is the frequency of the reflected signal?
+/- 63MHz compared to the interrogator signal
Where are DME/Ps used?
In MLS
What is the pulses per second (pps) of the ground station?
2700pps
What is the pps of each aircraft?
27pps
What is usual number of max aircraft per DME?
100 (2700/27)
What signals are dropped first when a DME becomes saturated?
The weakest signals
Describe search mode
150pps for 10 seconds, then 60pps for 30 seconds and then 30pps thereafter
Describe tracking mode
25pps
Describe memory mode
For seconds after signal loss, DME freezes and returns to search mode
Describe the identification of a DME
Station transmits 3 letter idents every 40 seconds
Describe the identification of a DME when co-located with a VOR?
- VOR ident x3 at low frequency
- DME ident x1 at high frequency
What DME range limited to?
Line of sight
What is the accuracy of a DME before 1st Jan 1989?
+/- 0.25nm and 1.25% of slant range on 95% of occasions or more
What is the accuracy of a DME after 1st Jan 1989?
Max error of 0.2nm
When is the only time groundspeed is correct when using DME?
When tracking directly to or from the DME station
What is read by the DME if directly overhead the ground station?
Altitude
