Timing not authorized for non-precision app ?

[Vincent340]

Hi all,

In some non-precision approach, the timing is not authorized (N/A) ? (ROD/gradient table in approach charts)

Is someone know why ?

Thank for your reply,
Vincent.

[Spitoon]

At least in some cases it's because there is some obstruction near the procedure and the positional accuracy of a timed leg is not good enough to provide the necessary protection.

[rennaps]

Spitoon that is correct

In 99.9% of the cases where timing is not approved it is an obstacle in the missed approach. With timing the tolerance of the missed approach position is so large. This then makes the latest start of climb position a lot further forward. This subsequently gives less distance to climb to get over a critical obstacle in the missed approach and would consequently raise the minimums.

[Vincent340]

Hi,

Thanks for your replies.

If the timing cannot be used in cases of obstacles, I need more information about the example below :

AirNav: KHUT - Hutchinson Municipal Airport (http://www.airnav.com/airport/KHUT)

- In the VOR approach 04, the approach can be timed. MAP procedure toward obstacles (obstacle 1739+/- depicted only on 22!)

- VOR/DME approach 22, MAP out of obstacle, but no timed approach.

The differences are :

- Reference to start the timing on VOR 04 (5,1 nm to MAP)
- enought margin in distance and/or altitude for a timed approach (only 500ft of difference on VOR/DME 22 from TURKY).

Am I right if I said that non-timed approach are based on those differences ?

Strange that there are lot of example that cannot explained a timed or non-timed approach.

[Vincent340]

Hi,

Just read the regulation and techniques concerning the CDFA.

Here is I can read :

<<The designated final approach segment minimum of 3 NM, and maximum, when using timing techniques, of 8 NM.>>

That could also a limitation of using a timed approach concerning also classical non-precision approach.