NZFF

Hi guys,

During a VOR approach, without a DME, how do you tell at what point you may descend to the MDA? Take a look at the Christchurch VOR approach for runway 02. The glideslop doesn't begin untill 3.2 miles after Burnham, your last referance point would be Burnham, begining descending from Burnham could mean descending below 1200 before 5 miles DME.

What is the correct procedure for a VOR, approach without a DME?

Thanks
James

The tool you use is Time...

You would have to time yourself and, using your groundspeed, calculate how far you have moved... looking at the tutorial here, the US plates have timing info for you... however the NZ AIP does not appear to have this... perhaps they only do a VOR approach with radar vectors?

Tricky these ones.
There are 2 methods.
The first is timing. Get down to minimum commencement altitude (2000 ft in this case) prior to Burnham.
First of all as you have no DME you will need to calculate your GS. Have a listen for the 2000 ft wind (most ATIS's will have a 2000 ft wind given) and then work out the Headwind component. Apply this to the IAS to get a Ground speed. 90 kts equals 1.5 nm/min, 120kts = 2 nm/min 150kts = 2.5 nm/min.
Looking at the chart you have approx 3 nm after passing BU NDB before you start the descent from 2000ft. Assuming you are travelling at 120 kts GS that will take 1.5 min. Start the timer crossing BU and after 1.5 min descend at an approx 3 degree slope. This is determined by halving your groundspeed and then adding a zero on the end. 120 kts = 600 fpm. In fact with this type of approach you may want to increase that rate slightly so that you get visual before the missed approach point (the VOR). Keep an eye on the time as each minute that passes you will travel 2 nm. The distance to the MAP is about 8.2 miles so after 4 min you should be getting close to the MAP.

The other is to raise the initial approach commencement altitude so that you have a 3 degree slope all the way down. The distance to the runway is 8.7 nm from BU. 8.7 x 3 = 2610 ft plus the elevation of 123 ft = 2733 ft. Lets call it 2700 ft.
The idea is to cross BU at 2700 ft and then descend on a 3 degree G/slope. Once again half the GS and add a zero on the end. Start the timer crossing BU and after every 1 min you will have travelled 2 nm. Make sure that after 1.5 min you are not below 1200ft.

The obstacle clearances are fairly generous so as long as you fly conservatively and aim to approximate a 3 degree G/slope then you will be fine.

It is a bit of a hit and miss procedure if you can excuse the pun.