CAS Base Level Crossing

[whowhenwhy]

One question that always gets asked in mil circles and is never answered satisfactorily is what type of service should you give a pilot if he is crossing at the base level of an airway, if it's defined as a flight level? Just wondered!

[Findo]

Interesting question.

My stab at it would be -

a. If you are an automous radar unit with the authority to work inside that airspace then it has to be a Radar Control Service as the a/c is inside controlled airspace. But then how do you apply the maxim that says inside and outside CAS are considered as separated ? Presumably you have to tell the pilot that standard separation may not be applied. :eek:

b. If you are not an automous radar unit you don't give a radar service as you do not have the authority. :{

[whowhenwhy]

See the separation issue is the biggy here. A mil pilot can conduct a base level crossing of an airway, as long as it is expressed as a FL, without speaking to anyone. However, if we were working that ac, at the base level under a RCS, then you'd only have 500' separation (or possibly less) against stuff below the airway. That doesn't work! Any more ideas anyone?

[zkdli]

For an a/c crossing the base of an airway where the base is expressed as a flight level, the books only refer to the a/c or pilot. There is no reference to atc crossing at this point. However, when I was doing this under the old bravo one, we used to continue to give whatever radar service the a/c had agreed with us.
The a/c is not under radar control, because the pilot is entitled to cross at this level without any type of service whatsoever in any flight conditions!
The a/c flying on the airway at the base plus 500' is where the problem arises and this where you can have some fun on oral boards!!

I know this doesn't really help, but some things in life are just not black and white, and while there is not a radar crossing service available to every a/c on every airway, there will be rules such as this one to allow people to achieve their goals.

[Findo]

whowhenwhy - not sure if you are saying this as a military ATCO. All aircraft, not just mil, can cross at the base Flight Level. There are only 3 types of Radar Service and you cannot provide RAS or RIS in controlled airspace so I go back to -

If you are allowed to operate in the airspace then you provide RCS. Separation may well be reduced as it can easily be on the edge of CAS when you don't have 5 or sometimes even 3 miles lateral against traffic outside. If you and/or the pilot are unhappy about giving traffic information only then you climb to at least 1,000ft inside.

If you are not allowed to provide a service inside that CAS then you terminate the service until clear of the airway.


zkdli - if the rules say the pilot does not need a radar service as in Class D and e airspace then you don't need give one. However if you do provide a radar service inside CAS it can only be RCS. :\

[DFC]

"Where the proposed ATS Airspaces adjoin vertically, i.e. one above the other, flights at a common level would comply with the requirements of, and be given services applicable to, the less restrictive class of airspace. In applying these criteria, Class B shall therefore be considered less restrictive than Class A airspace; Class C airspace less restrictive than Class B airspace, etc".

From a pilot's point of view, the above quote from Annex 11 is what we operate by (There is no difference filed by the UK).

When in the UK, the only extra requirement is that the Authorities have "Requested" that pilots refrain from cruising at the base level and along the alignment of an Airway.

Thus, the base level of an Airway in the UK is considered Class G and if we are getting a RIS or RAS or even FIS, we do not expect any change in service as we cross the base at 90 deg.

Regards,

DFC

[BuzzLightyear]

Findo

If they cross the airway at the base flight level then they are not technically WITHIN Class A airspace. So whether the service is being provided by an autonomous radar unit matters not a jot. RAS or RIS would be the appropriate service.

Being as a lot of bases give at least 500' separation from the lowest whole level within the airway, then the answer is to provide essential traffic information and if necessary take the appropriate remedial action if requested by the pilot.

If you look at the bases they are (or would have been in the mists of ancient time) decided so that a pilot crossing at right angles would have 500' separation from traffic inside under the Quadrantal Rule. Hence why the same rule of crossing does not apply when the base of the Airway is defined as an altitude.

Feel free to scour the AIP and find one that doesn't and prove me wrong :D

[DFC]

The problem with crossing the base of an airway defined as an altitude in the UK is caused by the Regional Altimeter Setting Region system of operation.

One could find that if an aircraft attempts to cross at the base altitude but is using the regional QNH, the aircraft may well be within the airway if the base level of the airway is defined using a local or adjacent TMA QNH........example the former G1 weat of the London TMA.

A simple answer in todays system is to scrap the RPS system in most of the UK and designate a conveniently located airfield or met reporting station (with an ATIS) that would provide the actual QNH to be used in a certain area.

This would make the appropriate and up-to date QNH far more available........I have waited for 15 minutes on London Info for just an RPS due to R/T congestion.

Regards,

DFC

[BuzzLightyear]

DFC

Surely most of the airfields round there have an ATIS?

I was always under the impression that you have to be in contact with the controlling authority to cross at the base when it is an altitude anyway haven't you? And they would give you the correct QNH on initial contact...or should anyway.

Might be wrong of course :D

[zkdli]

Another problem with crossing the base of an airway that is expressed as an altitude is that it might be above the transistion alt and you should be flying on the standard pressure setting not the rps. In the UK you are not allowed to cross at the base when it is an alt.

And thanks to everyone who found the relevent reg for providing a ras or ris to base crossers!!
I couldn't remember, it was a long time ago:O

[DFC]

Buzz, you are totally correct.

However, the system as it stands is far from safe.

Example 1 -

VFR flights are not required to cruise at a Quadrantal level. VFR flights are also not required to set 1013 when above the Transition Altitude.

Consequently, there is a high probability that an average VFR pilot will at some point each year forget to reset 1013 and adjust level before crossing at the base of an airway defined as a Flight Level.

The fact that this is seldom reported I believe is because;

a) Much of the airways workload at the distances from TMAs where the base of airways is in the flight levels, is at higher levels and there is few if any low and slow possible conflicts that bring the controllers attention to the bust when that attention is busy elsewhere.

b) VFR pilots ( by luck, and UK weather) for the most part cruise at the lower levels (3000ft and below).

Example 2 -

A VFR pilot sets the regional QNH and in keeping to the rules, flies at 4450ft below the base of an airway where the base is 4500ft.

All very nice until we check the regional QNH and find that it is 4mb lower than the QNH being used by the traffic on the airway!!!

30ft/mb erodes that 50ft....or even 100ft and places the flight within the airway despite being operated in accordance with the rules.

Regards,

DFC

[FJJP]

Dredging my sole remaining brain cell, I seem to remember that ac flying on airways NEVER used the base level. This was because ANY ac could cross the airway at base level without any kind of ATC service.