DGCA Air Navigation: Vdf Questions
137 exam-style Vdf questions for the DGCA Air Navigationpaper (CPL & ATPL). The first 12 are free below with answers and explanations — sign up free to practise all of them with progress tracking.
- Q1
What is the approximate maximum theoretical range at which an aircraft at FL130 could receive information from a VDF facility which is sited 1024 FT above MSL?
- A180 NM
- B 220 NM
- C120 NM
- D150 NM
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Correct answer: A. 180 NM
Maximum VHF/line-of-sight range is about 1.23 times the sum of the square roots of the two heights in feet. With 13 000 ft and 1024 ft this gives 1.23 x (114 + 32), approximately 180 NM.
- Q2
The maximum theoretical range at which an aircraft at FL80 can obtain bearings from a ground VDF facility sited 325 FT above MSL is:
- A 134 NM
- B158 NM
- C107 NM
- D 114 NM
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Correct answer: A. 134 NM
Range is 1.23 times the sum of the square roots of the heights in feet: 1.23 x (root 8000 + root 325) equals 1.23 x (89.4 + 18), about 134 NM.
- Q3
What is the minimum level that an aircraft, at a range of 113 NM, must fly in order to contact the tower on R/T for a VDF bearing from an airport sited 169 FT above MSL?
- A FL60
- BFL50
- C FL80
- D FL100
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Correct answer: A. FL60
To achieve line-of-sight over 113 NM to a facility at 169 ft, the aircraft height needed from the range formula is about 6000 ft, so the minimum usable level is FL60.
- Q4
What airborne equipment, if any, is required to be fitted in order that a VDF let down may be flown?
- AVHF radio
- B VOR
- C none
- DVOR/DME
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Correct answer: A. VHF radio
A VDF let-down needs only a serviceable VHF radio in the aircraft; the direction finding is performed by the ground station, so no special airborne navigation equipment is required.
- Q5
Which of the following is an advantage of Ground/DF (VDF) let-down?
- A It only requires a VHF radio to be fitted to the aircraft
- BIt is pilot interpreted and does not require the assistance of ATC
- C It does not require any special equipment to be fitted to the aircraft
- D It does not require any special equipment, apart from a VHF radio, to be installed in the aircraft or on the ground
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Correct answer: A. It only requires a VHF radio to be fitted to the aircraft
The advantage of a ground DF (VDF) let-down is that it requires only a VHF radio in the aircraft, with all the direction finding done on the ground, so no dedicated navigation receiver is needed.
- Q6
In which one of the following circumstances is ground direction finding (VDF) likely to be used to fix an aircraft's position?
- AWhen using the emergency VHF frequency 121.5 MHz
- BOn first contact with ATC on crossing an international FIR boundary
- CWhen contacting ATC to join controlled airapace from the open FIR
- DWhen declaring an emergency on any frequency
Show answer
Correct answer: A. When using the emergency VHF frequency 121.5 MHz
Ground direction finding is typically used to fix or assist an aircraft when it transmits on the emergency VHF frequency 121.5 MHz, allowing the ground station to obtain a bearing.
- Q7
An aircraft has to communicate with a VHF station at a range of 300 nm, if the ground station is situated 2,500' amsl which of the following is the lowest altitude at which contact is likely to be made?
- A190'
- B1,378'
- C36,100'
- D84,100'
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Correct answer: C. 36,100'
This Explanation is Coming Soon
- Q8
When would VDF be used for a position fix?
- AWhen an aircraft declares an emergency on any frequency.
- BWhen first talking to a FIR on crossing an international boundary.
- CWhen joining controlled airspace from uncontrolled airspace.
- DWhen declaring an emergency on 121.500 MHz.
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Correct answer: D. When declaring an emergency on 121.500 MHz.
This Explanation is Coming Soon
- Q9
Class ‘B' VHF DF bearings are accurate to within:
- A+ - 1°
- B+ - 5°
- C+ - 2°
- D+ - 10°
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Correct answer: B. + - 5°
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- Q10
What equipment does an aircraft need when carrying out a VDF letdown?
- AVHF radio
- BVOR
- CVOR/DME
- DNone
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Correct answer: A. VHF radio
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- Q11
An aircraft at altitude 9,000 feet wishes to communicate with a VHF/DF station that is situated at 400 feet amsl. What is the maximum range at which contact is likely to be made ?
- A115nm
- B400nm
- C143nm
- D63.5nm
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Correct answer: C. 143nm
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- Q12
Which of the following is an advantage of a VDF let down?
- Ano equipment required in the aircraft
- Bno special equipment required in the aircraft or on the ground
- Conly a VHF radio is needed in the aircraft
- Dit is pilot interpreted, so ATC is not required
Show answer
Correct answer: C. only a VHF radio is needed in the aircraft
This Explanation is Coming Soon
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