For anyone considering making a descent into an airfield with no instrument procedures please considder the following;
The legal requirment is that when IFR the aircraft must at all times be 1000ft above all obstacles within 5nm of the aircraft. The only exceptions to this are when following a published approach procedure or when visual and below 3000ft.
This means that if for example you decide to orbit your destination and descend as low as possible you are going to have to use the offical tolerances for VOR/NDB/DME which can cause a circle of error of some 2 to 5nm depending on how far you are away from the beacon(s) but let's say you are relatively close and the 2nm error applies..........Then you are going to have a turn radius of about 1nm around the airfield so that is now a circle of 3nm (6nm if a distance from the beacon). To this add the required 5nm for obstacle clearance bringing the circle to 8nm (11nm if a distant beacon).........Then allow for how acurate you fly so add on another 1nm for a proficient IR holder using a VOR/DME or another 3nm to 5nm for an IMC holder using crosscuts...........this brings the circle out to some 11 to 14nm.
A circle of 11 to 14nm around the destination could describe the area within which you must check for any obstacles and remain 1000ft above those obstacles to remain safe and legal.
Sounds a lot yes? But noe of that allows for wind drift while you fiddlw with the cross cuts or make sow's ear of the orientation!
Of course with say an NDB on the airfield then that circle could shrink to about 7 to 8nm for a slow aircraft.
However, when looking at the 1:500000 for obstacles remember that no terrain below 500ft is shown and no onstacles below 300ft AGL are shown. Thus you can have an unmarked 499ft hill with a 299ft mast on top. Most people understand that but remember that a place betwen the 500ft contour and the 1000ft countour could be 999ft tall with a 299 ft mast and right next to the 500ft contour cause it is a cliff!!!!!!!!
Airfields with instrument procedures spend thousands on accurate surveys...........even the 1:25000 Ordnance survey maps do not provide enough info for making a descent as low as 900ft AGL!
If you intend to fly IFR IMC at any stage and the destination does not have an IAP then the destination must have a ceiling above the MSA for -1 hr to +3 hours of ETA and you must have an alternate planned which has an IAP and is at the appropriate alternate minima!.
The most dangerous use of an IMC rating to ad-hoc IMC flying (not planned pre-flight).
Regards,
DFC