I am planning to take off from the top of a 20 story building for work. I have never done this before and wanted to get feed back regarding the setting for RTH and any other thoughts from pilots who do this alot. At start up will the Altitude read zero or will it read the real altidude that I am at roughly, 240ft AGL. The roof area is large so there is plenty of space if god forbid RTH is needed. There are no antenas or other hazards. I just want to make darn sure I set the RTH to the right height.

I also plan to have someone below to make sure the area is clear beneath where we are flying as a safety measure. To get the shot we need we will be out over the edge about 20- 30 feet.

Your input is greatly appreciated.

In which country are you planing this operation.  If its UK you will need to complete a full risk assessment, which if in a built up area you may require it to be undertaken on a Sunday morning perhaps when least amount of persons are about and least amount of traffic in the streets below.  Also you may need more than one person on the ground and certainly will need two-way radios to keep in contact with Observer on the roof who will keep the Pilot informed.  Obviously you will I assume have your commercial CAA approval if in the UK.  Have you considered a specific flight path, orientation from the roof to ensure the aircraft does not go unnecessarily close to other buildings, so the aircraft whilst in the air is always within a specified segment of airspace; consideration of alternative landing site.  Lots to think about and dont forget to notify local ATC for consent especially at high altitude where helicopters could operate, probably best to give ATC specific time frames.
When it takes off that will be the height to which your return home height be set.  So if you are 20m up from agl and the aircraft drops to 5m agl,  when it enters rth mode it will rise to to 15m to the set height of 20m agl,  before heading home.

Other factors you might wish to consider are:

1. The metal in the building's structure may cause some issues with compass calibration.

2. If there is any wind, then you can expect rising air on the windward side of the building, sinking air on the leeward side of the building, and some "curlover" just downwind of the windward edge of the building -- which might be directly above your take-off point.

3. I suspect you will encounter less turbulence if you do a vertical ascent/descent above the takeoff point rather than a slant ascent/descent.

As GB44 said, the I1 will not know it's on the top of a building. The pressure transducer used for altitude sensing will simply use the setting for the take-off point and all heights will be relative to that. So an RTH of X meters will be X meters above the take-off point.

ajohnsonlaird Posted at 2015-6-20 03:50
Other factors you might wish to consider are:

1. The metal in the building's structure may cause so ...

Thank you very much for your input. This community of pilots is awesome!

GB44 Posted at 2015-6-20 02:41
In which country are you planing this operation.  If its UK you will need to complete a full risk as ...

Flying in the USA. Thank you for your input. You are Spot on. We will be doing this on a Sunday. I will be the dedicated pilot. We have a dedicated cameraman. A spotter in the roof with us and a spotter below. We have an emergency landing spot which will be the top of the buildings parking garage. Also we will have a planned out flight path for the shots and will not fly outside the property lines of the developement. The tower is not open yet so any pedestrian traffic below can be managed. Thank you for your input. Cheers!

Sounds like it will be quiet the show, do post pics if you can!

Is it the highest roof around?   If so then I wouldn't set the RTH too high as it will just fly up for no reason.  But if you need to clear anything else make sure it's high enough, otherwise I'd set it for 20 feet or so.

gatorone30@hotm Posted at 2015-6-20 06:26
Flying in the USA. Thank you for your input. You are Spot on. We will be doing this on a Sunday. I  ...

You may also want to give a pre-flight briefing to all those present, the complete crew set.  For example if you shout out Dead Stick to make all aware of a potential failed engine, what does that mean exactly to them.  Well it means they must run !!  But you know what I mean, provided you have a good pre-flight induction with everyone so they all know the emergency procedures this will also help with your risk assessment compliance.  

PM me with your direct email, if you want some sample Risk Assessments.

Otherwise Good Luck and stay safe my friend.

Love to see some finished shots.

Also bear in mind if the RTH is activated less than 20m away it may just try to land vertically at that location.  Obviously this is not good if it is 10m away from the edge of the building, as it will then be heading towards the pavement 120m below or whatever the height is.  You may have some comfort if you have a tether on the aircraft, then there is no way it is going to end up on the pavement below.  Downside is then you have to make sure the shoot doesn't get the tether in the frame, but there are ways around that also.