Ground Obstacle Clearance on a visual approach

[your_dreamguy]

Under FAR 121 you are required to be at or above the VASI (visual approach) or the ILS G/S or G/P (instrument approach) while coming into land at a runway. However, what if you are conducting a visual approach to a runway where there is no visual aid or instrument aid? My training instructor said that you still need to maintain a 3 degree or greater glidepath to the runway. However, I cannot find a reg which states that. Further, to be certified for takeoff obstacle clearance under the FAA that same runway would need to have a 48 feet/NM obstacle clearance path in front of it. Therefore, in theory, wouldn't you just need to maintain 152' per NM coming to land? Note: 152' per NM is 200' per NM S/E climb gradient - 48' per NM obstacle clearance? Example, you are coming in to land at a runway which is sea level. This imaginary runway has no visual or instrument aid. My instructor would argue you would need to be at least 300 feet per NM or greater coming into land visually (i.e. at 3 NM out, you would need to be 900' above TDZE or greater). I am suggesting that you would need to be at least 152 feet per NM or greater coming into land (i.e. at 3 NM out, you would need to be at least 456' AGL or greater and that would still be legal).

Chime in.

 

[atrdriver]

I don't have time to look at the regs, but lets put it this way. If you are taking a checkride and have a fed in the sim, and you're 456' AGL at 3 miles on a visual, you will bust the ride. You are expected to be at 900' at 3 miles, 600' at 2, etc.

 

[wmuflyguy]

I believe that it is just the expected norm to maintain a 3 degree guide path on a visual, because most vasi and papi's are set at 3 degree's.

As for the Obstacle clearance plain argument wouldn't always save you on an approach, becaase single engine procedures or obstacle departure procedures are not alway straight out and the terrain on the runway centerline can be significantly higher than the 200' nm plain.

 

[DrewBlows]

Be good to the airport neighbors and fly a 3 degree glide path. You will be higher with less power when you fly over their house with a 3 degree glide path. You really don't want to field calls to explain why you were only 1000' above the ground six miles out with a high power setting.

 

[your_dreamguy]

Replies

ATR Driver,

Thanks for your reply. I still haven't found anything. I think you can go below the 3 degree G/P legally. For example, conducting a non-precision approach. On the final descent to MDA, you may arrive to the MDA below the 3 degree G/P. Further, you could proceed to land at the runway, provided you just kept obstacle clearance. Even though it would be proper technique to level out at MDA, proceed to the VDP and then descend to the threshold...I don't see any regulation saying that technique is mandatory.

 

[Cardinal]

The legal requirement as I see it is "don't hit anything." The practical requirement (as you've discovered) is not to get harrangued for careless and reckless. Lousy example: Over-the-top visual into Telluride. Cross the 14,000' mountain at 1 foot AGL, and you still have to descend grossly in excess of 3 degrees all the way down to make the runway.

 

[pkober]

The 200 ft/nm & 152 ft/nm criteria are only for departures from instrument runways. If you are flying from a field with no instrument procedures, than there is no required climb gradient. The FAA doesn't go out and determine climb gradients if there are no instrument procedures available. If a field has instrument departures there may also be higher climb gradients published.

Also those numbers are for departures only, not arrivals. Simply using 200 ft/nm on a arrival to a viz only field may run you into a tower or mountain. If you fly for an airline it would probably be hard to find an airlport that you fly to that doesn't have an IAP.

3 degree visual GP will always keep you out of trouble on most arrivals, unless obstacles are present. It's more predictable and it's easy to manage your energy on a 3 degree GP.

 

[buckets]

Remember, the reg also states that you hold the appropriate glidepath until a "lower altitude is necessary for a safe landing!" This is where the real argument is - when do you determine the need to go to a lower altitude to make the touchdown zone of the runway? 1 mile out? 3 miles out (Aspen)? Most landing distance are based on TCH of 50'. Have fun out there! If you don't hit anything on final - you are successful!

 

[AA717driver]

'Don't hit nothin' because you're too low and don't bust your op spex by being unstable cause you're too high.

I'd crash just trying to do the math to figure out the altitudes for a 3 deg. slope.

This isn't rocket science (unless you're JAA...). TC

 

[pipe]

That 152' nm is to clear all obstacles by a grand total of one nanometer.