AGL or AMSL

[Tim Mackey]

We all know ( or should ) that there are restrictions on altitude based on aircraft weight. However, what I confess I'm not clear on is whether the quoted height limit is above sea level, or ground level where the pilot is. This could clearly have implications for slopers of certain models.
The Orme for example is 700 ft at the peak, and around 550 feet where we normally fly
In summary, as I understand it, the limits are....
1) Under 7kg - no limit
2) 7-20 kg - 400 feet ( now including pure gliders since a few years ago )
3) 20kg+ errrr, that's not a model aeroplane anymore its a light aircraft and you'd better be familiar with ALL the CAA rules and regs, as well as LMA approval of model and pilot etc.

So, for 2)...... sea level or ground level? My assumption is sea level.

Edited By Tim Mackey on 19/05/2012 21:19:54

[John Privett]

Has to be ground level, surely? Otherwise there's loads of places you wouldn't be able to fly a 7kg+ model at all.

The 400 foot limit exists to maintain separation between models (over 7kg) and full-size traffic. Full-size traffic has to obey "Except with the permission in writing of the CAA, an aircraft shall not be flown closer than 500 feet to any person, vessel, vehicle or structure."

[Tim Mackey]

Yeh, Im leaning toward GL now, as a response on our club forum to the same question suggests its GL.

You would think that it was clearly spelt out in BMFA CAA documentation though eh

[John Privett]

Tim, this may help. Specifically, chapter 2 page 2 where 4.2.2 is headed Article 166 - Small unmanned aircraft and para 4 says;

(4) The person in charge of a small unmanned aircraft which has a mass of more than 7 kg excluding its fuel but including any articles or equipment installed in or attached to the aircraft at the commencement of its flight, must not fly the aircraft:
(a) in Class A, C, D or E airspace unless the permission of the appropriate air traffic control unit has been obtained;
(b)within an aerodrome traffic zone during the notified hours of watch of the air traffic control unit (if any) at that aerodrome unless the permission of any such air traffic control unit has been obtained; or
(c) at a height of more than 400 feet above the surface unless it is flying in airspace described in sub-paragraph (a) or (b) and in accordance with the requirements for that airspace.

Edited By John Privett on 19/05/2012 21:35:31 (just re-aligning the line-breaks!)

Edited By John Privett on 19/05/2012 21:36:26

[Simon Chaddock]

But if you fly a +7kg plane out more than 500ft horizontally from your elevated position then surely the 400ft limit applies.

[Alan Cantwell]

the gliding thing is interesting, with the new regs for over 20kg gliders, bringing the inspection in line with powered over 20kg, they would be useless at 400feet, needing to get up there an seek lift, either from an aerotow, or slope, makes you think

[David Gilder]

Posted by John Privett on 19/05/2012 21:25:41:

"Except with the permission in writing of the CAA, an aircraft shall not be flown closer than 500 feet to any person, vessel, vehicle or structure."

(Unless you are in one of the specified LFA's (Low Flying Areas) 14T or 20T, and flying Military Aircraft) where there are cleared down to 250 ft!! These heights are known as MSD's (minimum seperation distances) and are effectively an imagianary bubble around the plane in all directions to the specified distance!

In the case of the AGL or AMSL, it will refer to AGL with GL being the level that the Take Off and Landing Zone are sited at (assuming that both are one and the same)!

Hope that makes it all as clear as mud pie for you all!!!

Dave - (AGL/AMSL/MSD dept!)

[Martin Harris - Moderator]

I'm fairly sure that I've seen a definition somewhere that it's 400 feet above the point of launch which would be very relevant for slope soarers.

The point of the 400 foot restriction outside controlled airspace (where you can fly to any height agreed with the local Air Traffic Control) is to give a nominal 100 foot clearance to a full sized aircraft complying with the 500 foot rule so it's assuming the pilot will be somewhere close to the model and any aircraft will be at least 500 feet above them.

Edit:

Found it in CAP 658 Chapter 5 Safety Considerations

Additional Requirements – Models Having a Mass from 7 kg to 20 kg
Should only be flown
• Clear of controlled airspace unless with Air Traffic Control (ATC) permission.
• Clear of any Aerodrome Traffic Zone (ATZ) unless with ATC permission.
• At less than 400 ft above the point of launch except with permission as above.

Edited By Martin Harris on 20/05/2012 02:15:28

[Tim Mackey]

Thanks chaps, seems it is indeed above GL, as in launching point.

400 feet is not much at all really for largish models is it. I doubt my BUFF will exceed 7kg, but still glad then that my Spektrum altitude telemetry device sends data based on GL at launch

........and self calibrates every time I power up