Tinstaafl
Well-known member
- Joined
- Mar 15, 2003
- Posts
- 188
NDB/DME approaches aren't much different to VOR/DME approaches. All that changes is the azimuth aid. Australia has a lot of them. Bear in mind that the DME doesn't have to be co-located with the azimuth aid to have an xxx/DME approach - although that seems to be the common situation in the US.
A DME Home & Descent is something else entirely. It relies on nothing but a DME to home to the station, first establishing orientation then refining subsequent headings to achieve best rate of closure to fly to the DME beacon. A rate one turn was usually sufficient to get the general direction to the aid then you'd find & bracket the required heading by holding a heading & note the Rate of Closure. After getting an RoC turn L. (or R.) 30 deg & note RoC again. If RoC increased then turn another 30 deg. in the same direction. If ROC reduced then turn 60 deg the other way. Once the correct direction was found, keep doing the HDG adjustment/RoC check until RoC peaked & reduced. Make the next HDG adjustment 15 deg in the opposite direction. Every 5 or 10 mins (depending on distance &/or laziness) you'd redo the bracketing routine but now using 10 deg HDG adjustments followed by a 5 deg. correction after RoC drop. That was the homing part.
The requirement was to arrive within 2nm of the aid**, after which you'd turn to the the approach's charted outbound heading, fly out the required distance to an 80/260 procedure turn then return to the station. You had to arrive back within 2nm of the aid. There were descents in the approach procedure as well.
It's easy with modern DME displays that have groundspeed info but the old Oz specific DME (operated on 200MHz) originally didn't have that capability. You had to repetitively time yourself for each heading change to find the best closure rate. Easiest was to time for 36 sec then multiply the changed distance by 100 to get RoC. Those old displays used a dial rather than a digital readout so you had to pay attention.
**There were some 'cheats' though. I used to have a table that gave deg. to turn to get closer to the station depending on point of minimum closure eg min. closure = 10 nm turn 90 deg. If dist. increased turn another 180 deg. If dist. reduced turn another xx deg in the same direction. The 'xx' deg increase by 10 for each mile closer to the station the min. closure was. Can't remember all the details now but it wasn't too difficult to get within 1 nm.
It was important to get an idea of the wind direction during the homing stage so that you could lay off drift during the DME Descent out- & inbound legs ie the approach proper. Was Best RoC greater or lesser than TAS? which direction was the HDG adjustment trend
needed to maintain Best RoC? You could get a pretty good idea of wind velocity & compare it to the DME Descent HDGs for an out/inbound adjustment.
A DME Home & Descent is something else entirely. It relies on nothing but a DME to home to the station, first establishing orientation then refining subsequent headings to achieve best rate of closure to fly to the DME beacon. A rate one turn was usually sufficient to get the general direction to the aid then you'd find & bracket the required heading by holding a heading & note the Rate of Closure. After getting an RoC turn L. (or R.) 30 deg & note RoC again. If RoC increased then turn another 30 deg. in the same direction. If ROC reduced then turn 60 deg the other way. Once the correct direction was found, keep doing the HDG adjustment/RoC check until RoC peaked & reduced. Make the next HDG adjustment 15 deg in the opposite direction. Every 5 or 10 mins (depending on distance &/or laziness) you'd redo the bracketing routine but now using 10 deg HDG adjustments followed by a 5 deg. correction after RoC drop. That was the homing part.
The requirement was to arrive within 2nm of the aid**, after which you'd turn to the the approach's charted outbound heading, fly out the required distance to an 80/260 procedure turn then return to the station. You had to arrive back within 2nm of the aid. There were descents in the approach procedure as well.
It's easy with modern DME displays that have groundspeed info but the old Oz specific DME (operated on 200MHz) originally didn't have that capability. You had to repetitively time yourself for each heading change to find the best closure rate. Easiest was to time for 36 sec then multiply the changed distance by 100 to get RoC. Those old displays used a dial rather than a digital readout so you had to pay attention.
**There were some 'cheats' though. I used to have a table that gave deg. to turn to get closer to the station depending on point of minimum closure eg min. closure = 10 nm turn 90 deg. If dist. increased turn another 180 deg. If dist. reduced turn another xx deg in the same direction. The 'xx' deg increase by 10 for each mile closer to the station the min. closure was. Can't remember all the details now but it wasn't too difficult to get within 1 nm.
It was important to get an idea of the wind direction during the homing stage so that you could lay off drift during the DME Descent out- & inbound legs ie the approach proper. Was Best RoC greater or lesser than TAS? which direction was the HDG adjustment trend
needed to maintain Best RoC? You could get a pretty good idea of wind velocity & compare it to the DME Descent HDGs for an out/inbound adjustment.
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