Aircraft Hangar Apron Grades

[655321]

Does anyone have any words of wisdom on pavement grades for an aircraft apron for a Group 3 Hangar (small private aircraft)?

I found information on minimum grades; it seems that 1% to 1-1/2% are desirable minimums for asphalt and PCC. I gathered from one source that a min longitudinal grade of 1/2% for concrete can be done, but is tough to build. So that doesn't sound any different from car parking.

But I haven't found much on desirable grade breaks or maximum slopes.

Any insight would be appreciated. Thanks.

 

[CarlB]

Did you chech the FAA circulars? They cover all that.

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/MainFrame?

For large aircraft, 1% is the MAXIMUM apron grade.

 

[655321]

Thanks CarlB,

Here's a excerpt from FAA Advisory Cricular 150/5300-13, Chapteper 5, Page 54:

"To ease aircraft towing and taxiing, apron grades should be at a minimum, consistent with local drainage requirements. The maximum allowable grade in any direction is 2 percent for Aircraft Approach Categories A and B and 1 percent for Aircraft Approach Categories C and D. Where possible, design apron grades to direct drainage away from the any building, especially in fueling areas."

I didn't find anything specifically regarding grade breaks on aprons - any advice?

 

[bimr]

You should also check the NFPA 409 Standard of Aircraft Hangers and NFPA 415 Standard on Airport Terminal Building, Fueling Ramp Drainage, and Loading Walkways. Specific slopes are called for in these documents. For example:

5.11 Drainage of Aprons and Hangar Floors.
5.11.1 Apron Drainage.
5.11.1.1 The apron or approach at the entrance to the hangar shall slope away from the hangar with a minimum grade of 0.5 percent (1:200) for the first 15 m (50 ft).
5.11.1.2 Ramps used for aircraft fueling adjacent to hangar structures shall comply with NFPA 415.
5.11.1.3 In establishing locations for nearby aircraft parking, consideration shall be given to the drainage pattern of the apron.

The US government has guidelines on drainage slopes:

http://www.wbdg.org/ccb/ARMYCOE/COETM/ARCHIVES/tm_5_820_1.pdf

1) Minimum slopes. For satisfactory drainage of airfield pavements, a minimum gradient of 1.5 percent in the direction of drainage is recommended except for rigid pavements where 1.0 percent is adequate. In some cases, gradients less than 1.5 percent are adequate because of existing grades; arid or semiarid climatic conditions; presence of noncohesive, free-draining subgrades; and locations of existing drainage structures. Such factors may allow a lesser transverse slope; thus, construction economies are effected and preferred operational grades are obtained.

 

[jartgo]

I agree with CarlB. I know FAA 5300 says 2% max, but the users of the apron will not be happy with that. 1.5% should be the maximum and when it's used, there should be some physical limitation as to why it needs to be that steep (i.e., tying to existing grades). In most circumstances 1% max is what I've used even for small planes. Keep in mind they will likely be pulling the small planes around by hand on the apron at times and you don't necessarily want to be pulling it up any kind of slope.

On the other hand, it's difficult to find a paving contractor that will do less than 2% with asphalt...it's just too flexible of a material to get the grade that tight without leaving birdbaths. Concrete is the way to go with aircraft aprons.

Having said that, I just did one in asphalt at 1% for small planes. I had the owner accept a birdbath disclaimer from the contractor...we couldn't afford concrete and the airport users understandably wanted it flat as physically possible.

In summary, normal considerations for drainage of paved surfaces don't necessarily apply to airports. Of course, these flat slopes may require that you put more thought into your drainage plan.

 

[sodengineer]

WARNING-SIDE NOTE!

If you have ever had to push a Cessna 182 back into a hangar, you know that .5% is the max you want to push. I'm not a small man, and it is about all I can do to push it back into the hangar. I don't know how the smaller women do it. I have actually looked into putting a winch in the back of the hangar to do the heavy lifting. Anything larger than a 182 would require two people.