Doc 4444, 5.7.1.2 - Question
 

Hello all,
Can you please explain the separation standard described in paragraph 5.7.1.2 in Doc 4444.

5.7.1.2 If an arriving aircraft is making a straight-in approach, a departing aircraft may take off:
a) in any direction until 5 minutes before the arriving aircraft is estimated to be over the instrument runway;
b) in a direction which is different by at least 45 degrees from the reciprocal of the direction of approach of the
arriving aircraft:
1) until 3 minutes before the arriving aircraft is estimated to be over the beginning of the instrument runway
(see Figure 5-38); or
2) before the arriving aircraft crosses a designated fix on the approach track; the location of such fix to be
determined by the appropriate ATS authority after consultation with the operators.

Thanks,

And what is that you don't understand?

I am not familiar with this separation, having retired 7 years ago. However, it appears to be a Procedural Separation.
It appears to apply in 2 separate circumstances ie. a) & b).
a) is quite simple, in that it can be used for a departing a/c , as described &
b) can be used in the 2 instances described in provisos 1) & 2).

This is used in procedural environment. If we start by looking into provision a) with the following example: Arriving aircraft is 7 minutes from the threshold of runway 29 with descend to 5000ft. Departing aircraft is cleared for take-off on runway 11 to 4000ft.
Provision a) allows for opposite departures but how is vertical change possible?
My understanding is that the departing aircraft can take-off below the inbound aircraft but another form of separation is required to climb through the arriving aircraft.

Doc 4444
 

I would agree with your interpretation of a). In your example the departure would be vertically separated underneath the arrival. Then you could use 5.4.2.3.4.2 to establish a pass and allow climb/descent. (Although with jets this is all going to happen pretty quickly and may not be practical.)

It is a case of one separation leads to another....

Not everything in DOC 4444 is straight forward. Even the Figure 5-38 introduces some items that do not match the text.

Most countries publish their own interpretations and these tend to be more practical. (Although not always). Take 5.4.1.2.1.2 a). (I have seen this interpreted in about 4 different ways in local ATC regulations.)

VOR: both aircraft are established on radials diverging by at least 15 degrees and at least one aircraft is at a distance of 28 km (15 NM) or more from the facility (see Figure 5-2);

Because of the word "diverging" some countries insist that it can only be applied to outbound aircraft. (This is supported by the Figure 5-2 which shows outbounds). Others apply this to IN/OUT and/or IN/IN. The distances and number of degrees used varies greatly as well.

I agree with the VOR separation that some places use 15NM for outb/outb, and 20NM for outb/inb or inb/inb.

The reason for this thread is actually provision b) where a departure takes-off using the duty runway and makes a turn which keeps him outside of the 45° of the reciprocal track of the arrival (see figure 5.38 in Doc 4444). Can the departure clearance be an altitude above the inbound if the clearance is only valid until 3 minutes before the inbound estimates to be over the threshold. Or does this paragraph only clear the departure aircraft below the inbound aircraft and when airbourne to come up with separation to allow the climb/descend through.

An example for b)

VOR Approach Rwy 28. (no DME). VOR located at 5 NM from the threshold 28.

Arrival making straight in. Departure to go RWY 28 on a track 280.

First what separation could you use without this one? Probably 10 mins longitudinal climbing same track is all you can find. Bit restrictive.

With the VOR as the designated point this allows you to get the departure airborne prior to the arrival checking the VOR. 3 minutes instead of 10....

This separation has probably been in the 4444 since the first day. (When DC6's ruled the world and NDBs were the main aid). Someone would have decided that this was safe.
You would have to watch the missed approach if the departure was slow.

In the new RNP/RNAV world I can imagine (in a procedural environment) that this will still apply with a point designated on the approach after which a departure cannot be released. Of course the computers will be managing that and it will vary for each combination of flights!:rolleyes: