Arrival/Departure Tower Separation in Low Cloud Conditions

[good egg]

I'd like to know what separation any tower units apply between Departures and Arrivals in Low Cloud (let's say OVC at 200ft) and what justification you have for that...e.g. MATS 2 entries.

Scenario:
Arrival aircraft at 4.5nm final. You line up a departure. You clear departure for take-off as arrival reaches about 3nm final. Given the low cloud you are not visual with the arrival.
The departure gets airborne in about 40seconds. By this time the arrival is about 1.5nm from touchdown. You clear it to land. The departure quickly disappears into cloud and the arrival is still not visible.
(1) What separation are you providing? (Both aircraft are not visible and you have less than standard separation)
(2) What allows you to do this? (Please provide references)

Thanks

[chevvron]

(1) Deemed.

[good egg]

(1) Deemed.

Great, and the reference for that is??

[ZOOKER]

'Morning good egg,
It's a long time since I did ADC, (we had OKTAS then), but I'm certain OVC at 200ft would have triggered what we used to call 'LVP Cloud'. I can't remember offhand what procedures this condition involved, but if the procedures still exist, and they may be 'aerodrome-specific', I'm sure someone will be along shortly with the answer.
The use of the ATM, (Aerodrome Traffic Monitor, - a small radar in the VCR showing the traffic within, say, 20nm of the ARP), may have a part to play?

I can't find the references at the moment. Most of it was contained, (I think), in our airfield's MATS Part 2.

[good egg]

Hey Zooker

That's great, but same would apply at OVC at 300ft...arrival still wouldn't be visually acquired until around 1nm from touchdown (assuming standard 3 degree glide, and good visibility)....departure would disappear shortly after take-off...so still less than standard separation.
In order to do this as Chevron pointed out there must be a 'deemed' separation between arrivals & departures? If so, is this a local separation standard? (I.e. MATS 2...and based on a local risk assessment?)

[ZOOKER]

Yes, I was just thinking about that scenario as your post above appeared.

[good egg]

Yes, I was just thinking about that scenario as your post above appeared.

Great minds? ;)

[ZOOKER]

It's a good 'oral-board' question, (if they still have them).
When we did our rating exams, there were books full of stuff that candidates had been asked on previous boards. These were the source of much interesting and useful discussion, regarding scenarios such as this.

[good egg]

If only someone knew the answer! :)

It's a good 'oral-board' question, (if they still have them).
When we did our rating exams, there were books full of stuff that candidates had been asked on previous boards. These were the source of much interesting and useful discussion, regarding scenarios such as this.

[5'n'3]

I have seen this kind of scenario handled differently depending on where in the world you are.

I have worked rules whereby if the arrival flight is within 5nm of touchdown, you cannot launch a departure unless you can apply reduced separation. On the other hand, I have worked at airfields where the scenario is completely disregarded.

The main issue in my opinion is that you have to plan for the event that the arriving flight goes around. In this situation, I have heard some people say that emergency separation may be applied as it is an unplanned event however,

My opinion is that assuming both flights are IFR and you are inside CAS, you should never put yourself in a situation whereby you cannot provide standrd separation in the event of the arrival going around. This can mainly be achieved by applying a form of departure separation to flight which is going around.

For example, if your departure routes on a SID which is separated from your Missed Approach procedure by 45degrees or more, you could argue a 1 minute split is acceptable and therefore, you can launch a departure when the arrival is more than 60 seconds from touchdown.

Alternatively you may elect to use a form of vertical if the departure is likely to have cleared your MAP altitude by the time the arrival reaches MAP.

Either way, (in my opinion) if you can't provide standard IFR separation or reduced separation between the two flights, you probably shouldn't be launching the departure.

[good egg]

Either way, (in my opinion) if you can't provide standard IFR separation or reduced separation between the two flights, you probably shouldn't be launching the departure.

Hmmmm, I think declared capacities at busy single runway airports would take a pretty big hit if you applied that logic.
I'd say it's one of those scenarios where you have to weigh up the risk of a missed approach.
Obviously in poor weather conditions arrival spacing would be increased to mitigate the risk of LOS/WVE between departure and subsequent missed approach.
However, in conditions where statistically the %age of missed approaches is very small I'd suggest it was reasonable to apply a "deemed" separation between departures and arrivals. [Providing controllers are aware of the risk and trained appropriately to resolve/restore standard separation]
Regardless of conditions the tower controller should plan what action to take if the arrival performs a missed approach.

I'm wondering if anyone has a specific entry in their MATS 2 relating to such a "deemed" separation?

[good egg]

Anyone...?

[HEATHROW DIRECTOR]

One at one end, the other at the other end = geographical separation!

But seriously, I have seen the situation a few times and used radar headings to separate the traffic without danger.

[zonoma]

Either way, (in my opinion) if you can't provide standard IFR separation or reduced separation between the two flights, you probably shouldn't be launching the departure.
5 'n' 3 - that would mean that you can only independently use two runways if they are located 5nm apart (or 10nm if you are in a region where 10nm is stipulated as the required radar separation), unless there is a superhuman way of controlling them by the same controller whereby you could reduce the distance to 3nm. I'm sure that would be fine at Heathrow, and still room for a 3rd.......

[HEATHROW DIRECTOR]

At Heathrow the AIR ARR and AIR DEP controllers sit next to each other each and will alert the other in case of a conflicting go-around.

[crsctl]

FAA standard

5−8−4. DEPARTURE AND ARRIVAL
TERMINAL. Except as provided in para 5−8−5,
Departures and Arrivals on Parallel or Nonintersecting
Diverging Runways, separate a departing aircraft
from an arriving aircraft on final approach by a
minimum of 2 miles if separation will increase to a
minimum of 3 miles (5 miles when 40 miles or more
from the antenna) within 1 minute after takeoff.
NOTE−
1. This procedure permits a departing aircraft to be
released so long as an arriving aircraft is no closer than
2 miles from the runway at the time. This separation is
determined at the time the departing aircraft commences
takeoff roll.
2. Consider the effect surface conditions, such as ice,
snow, and other precipitation, may have on known aircraft
performance characteristics, and the influence these
conditions may have on the pilot’s ability to commence
takeoff roll in a timely manner.

[good egg]

FAA standard

5−8−4. DEPARTURE AND ARRIVAL
TERMINAL. Except as provided in para 5−8−5,
Departures and Arrivals on Parallel or Nonintersecting
Diverging Runways, separate a departing aircraft
from an arriving aircraft on final approach by a
minimum of 2 miles if separation will increase to a
minimum of 3 miles (5 miles when 40 miles or more
from the antenna) within 1 minute after takeoff.
NOTE−
1. This procedure permits a departing aircraft to be
released so long as an arriving aircraft is no closer than
2 miles from the runway at the time. This separation is
determined at the time the departing aircraft commences
takeoff roll.
2. Consider the effect surface conditions, such as ice,
snow, and other precipitation, may have on known aircraft
performance characteristics, and the influence these
conditions may have on the pilot’s ability to commence
takeoff roll in a timely manner.

Thanks crsctl