As an example, at Heathrow the landing rate is ~45 aircraft an hour: if you put even one extra mile between those aircraft, you're looking at about 25 seconds extra per aircraft

 

 One extra mile isn't going to get you much. Standards differ around the world, but when moving from Cat I to Cat II/III operations, the spacing often doubles if not more so. The arrival rate essentially tanks.

 

 

One extra mile isn't going to get you much. Standards differ around the world, but when moving from Cat I to Cat II/III operations, the spacing often doubles if not more so. The arrival rate essentially tanks.

Exactly. My point was that even a seemingly tiny change like an extra mile -- which doesn't sound like much -- can result in massive delays. As I say, the CATII/III spacing in reality is usually going to be much more than that.

 

Hence why airports are generally reluctant to implement LVPs unless they really have to!

Just for clarity -- it's worth mentioning that the reason flights end up getting delayed or cancelled in bad weather is rarely to do with the weather itself (i.e. pilots/airlines saying "we're not flying in that!"), and more to do with the impact LVPs have on airport flow rates. If you have an airport operating at capacity and all of a sudden you have to extend the final approach spacing for each aircraft by a mile or two as part of the ILS safeguarding, departing aircraft have to use different holding points and taxi routes and so on, you can very quickly rack up a heck of a lot of delay -- which inevitably results in some flights dropping off the schedule altogether.

 

As an example, at Heathrow the landing rate is ~45 aircraft an hour: if you put even one extra mile between those aircraft, you're looking at about 25 seconds extra per aircraft -- do that for an hour or two (and bear in mind the minimum separation will likely be much greater than just one more mile than usual) and you'll have hours worth of arrival delays. Ultimately this eventually leads to diversions (when aircraft in the air don't have enough fuel left to keep holding) and aircraft being out of position, which subsequently results in delays and cancellations all over the place (and in some cases literally all over the world as the tightly-packed schedules for aircraft and crews begins to topple, domino-like).

 

Yeah, I should've been more clear there. Good job on explaining the TM issue there.

On a normal day  at Heathrow the landing rates are 40 -45/hr. On windy days this can drop to 32-38/hr. When the rates drops below 36/hr airlines have to cancel flights.
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/371860/15-operational-risk--airspace-resilience.pdf

ILS landing rates at Heathrow are;
 

LRVR between 1000m and 600m - 34 aircraft/hour
LRVR between 600m and 15-m - 24aircraft/hour
LRVR less than  150m - less than 20aircraft/hour

 

http://www.ead.eurocontrol.int/eadbasic/pamslight-186011C629206B60A28097527AB5B92D/7FE5QZZF3FXUS/EN/AIP/AD/EG_AD_2_EGLL_en_2015-08-20.pdf

 

You need CAT III protection, which ensures that vehicles and other aircraft use the CATIII holding points further away from the ILS signal to avoid interference, as you obviously need the signal to be as accurate as possible. If Low Visibility Procedures are in force at the airport, CAT III protection will be available anyway but if you're practising autolands in CAT I or VMC minima, you should ask the controller for the protection if at all possible

As a general rule ATC will not protect the critical area's for a/c conducting a practice autoland or coupled approach. Different separation standards exist as well when operating Cat II or III with respect to both arrivals and departures.

Obviously they aren't going to increase separation for you and so a practice autoland is not really safe if closely following a previous arrival. But you should always inform ATC and request the increased hold distance. Otherwise a full autoland is not really safe. It's not always going to be possible for ATC to comply, especially at busy airports.

 

Coupled approaches are a regular occurrence with no special ATC restrictions. There's no intention to land automatically.

 

 

But you should always inform ATC and request the increased hold distance.

 

I suppose they might if they have no departing traffic. Would depend on where you are from a Country standpoint as well.

 

 

I suppose they might if they have no departing traffic. Would depend on where you are from a Country standpoint as well.

 

Arriving aircraft also have to kept futher from the runway in under LVP.

How do you mean Gerry?

 

 

How do you mean Gerry?

 

For CAT II/CAT 3 operations at Heathrow::

 

(e)  Pilots are to delay the call 'runway vacated until the aircraft has completely passed  the end of the green/yellow colour coded taxiway centre-line lights  

Ah sorry I see what you mean now.

Arriving aircraft also have to kept futher from the runway in under LVP.

 

 Well of course they do, I was referring to KevinH's reference of "But you should always inform ATC and request the increased hold distance." when doing practice autolands.

 There's so much more to protecting the critical area than keeping aircraft at the Cat II hold line. If the airport is not advertising Cat II or III operations, then you aren't going to have the Critical Area protected to Cat II standards.

 Well of course they do, I was referring to KevinH's reference of "But you should always inform ATC and request the increased hold distance." when doing practice autolands.

 There's so much more to protecting the critical area than keeping aircraft at the Cat II hold line. If the airport is not advertising Cat II or III operations, then you aren't going to have the Critical Area protected to Cat II standards.

 

Correct.

 

Also, full names - first and last - in the forum, please.

Well of course they do, I was referring to KevinH's reference of "But you should always inform ATC and request the increased hold distance." when doing practice autolands.

There's so much more to protecting the critical area than keeping aircraft at the Cat II hold line. If the airport is not advertising Cat II or III operations, then you aren't going to have the Critical Area protected to Cat II standards.

I mentioned the holding points, I didn't say that was all that was involved in CAT II/III operations.

 

I certainly wasn't suggesting that an airport would switch over to full CAT II/III operations in response. But if ATC do nothing then what is the purpose of informing them?

 

Maybe it varies from country to country?

 Point being that an inbound flight mentions that they are going to a practice autoland, it's the aircrew that needs to be wary that the ILS signal will not be protected like it would be if they were conducting Cat II operations. The tower may still taxi aircraft past the Cat II hold line, taxi aircraft across the runway, or continue departing well inside the point where they would have had to stop if Cat II or III were actually in place. 

 

I could see it very easily varying slightly from Country to Country.