VOR/DME fix with an unreliable ADF near Palmerston North
You are VFR from Napier (NZNR) to Palmerston North (NZPM) at 6,500 ft. You are 28 nm east of the Palmerston North VOR/DME. The VOR is selected to the 090 radial and the CDI is centred with a TO indication; your heading is 270°M. The ADF, tuned to the co-located NDB, shows a relative bearing fluctuating between 340° and 020°, with heavy static. A CB is reported 15 nm south. The Palmerston North CTR boundary is 12 nm ahead; you have not received a clearance. The VNC shows high terrain west of the CTR and a MBZ around Feilding. Fuel remaining is 38 US gal, burn 10 gal/hr, reserve 45 min. The GPS is serviceable but you have not entered a flight plan.
1. Interpret the VOR/DME fix and the ADF indications. What is your approximate position relative to the station and the CTR?
Read the worked answer
The VOR is selected to the 090 radial with a TO indication, and you are heading 270°M. The 090 radial is the locus of points east of the station, so you are on that radial, 28 nm east of the VOR/DME, tracking west toward the station. The TO flag confirms the station is ahead. The CTR boundary is 12 nm ahead, which places it about 16 nm east of the station; you are therefore about 12 nm outside the boundary.
The ADF should show a relative bearing near 000° if the NDB is co-located and you are tracking directly to it. Instead it fluctuates between 340° and 020°. Magnetic bearing to the station = heading + relative bearing: 270 + 340 = 250°M, or 270 + 020 = 290°M. The average is about 270°M, which agrees with the VOR, but the plus/minus 20° swing and heavy static show the ADF is not reliable for tracking. Use the VOR/DME as the primary fix and treat the ADF as a rough cross-check only.
2. Should you use the ADF for tracking? What action would you take regarding the control zone?
Read the worked answer
No. The ADF is being affected by precipitation static from the CB, and a 40° swing is not a stable tracking signal. Do not chase the bearing pointer. Maintain the VOR/DME track, and use the DME to monitor the CTR boundary: 28 nm east of the station means about 12 nm to the boundary. Call ATC before the boundary: '[Callsign], 12 nm east of Palmerston North, 6,500 ft, VFR to Palmerston North, request clearance into the control zone.' If clearance is not received, remain outside: turn 180° or orbit east of the boundary. Do not turn west toward the high terrain to remain clear. Also remain clear of the Feilding MBZ and the CB 15 nm south; a diversion north of track may be preferable to a southward deviation. The GPS is serviceable, but do not rely on it for airspace separation unless you have set up a relevant waypoint and confirmed the charted boundary.
3. If ATC asks you to hold outside for 10 min, calculate the fuel effect and state what you would monitor.
Read the worked answer
Fuel burn is 10 US gal/hr. Ten minutes of holding uses 10 x 10/60 = 1.7 gal. Fuel remaining becomes 38 - 1.7 = 36.3 gal. The 45 min reserve is 45/60 x 10 = 7.5 gal, so the margin above reserve is 36.3 - 7.5 = 28.8 gal. That is ample for the hold and the onward flight.
Monitor: time in the hold, fuel flow, and the DME distance from the VOR to ensure you do not drift into the CTR boundary. If the hold extends beyond about 20 min, recalculate the margin and consider diverting to an aerodrome outside the zone. Keep a listening watch on the ATIS and note any change in the CB or wind. If the ADF remains unusable, advise ATC that you are using VOR/DME only; this is useful if ATC intends to give you a radar vector or a position report.