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Which Approach


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Ok, The idea of an approach to descend to your landing spot keeping a constant path. This involves slowing your descent rate at the same time you are slowing your airspeed as you approach your spot. There is not one right approach for all situations, but generally there is one safer approach for each situation. I would like to get your opinion on which of the following two approaches you would use and why. If you think one of them is unsafe, or more unsafe, let me know that too. Also, if you don’t like either approach and have a better suggestion, I would love to hear it.

 

Ok, here we go. We are in a Schweizer 300C. Density Altitude is 6,400 feet. I don’t have the exact weight and balance stuff in front of me right now, but we have two 200 pound pilots, and about 20 gallons of fuel. When terminating either approach, we have full power and a very high collective setting to hover. I am not 100% now, but I don’t think normal hover work takes full power, but it is definitely up there. Now to the approaches:

 

#1: We turn final at 300 feet and 60 knots, slowing to 45 knots. We maintain this until the site picture is correct and initiate descent. We continue slowing as we descend. At about 150 feet AGL we are slowed to 35 knots. We cross through 40 feet AGL at 20 knots. We finish through, passing through ETL at about 20 feet AGL, and bring it down at a brisk walking pace from there.

 

The idea of the above approach is to bring the descent rate to a very negligible level to avoid coming down too fast and breaking through with a hard landing. The descent is gentle without the need to make a large power move, as you have your power in earlier.

 

#2: We turn final at 300 feet and 60 knots, slowing to 45 knots. We maintain this until the site picture is correct and initiate descent. We continue our descent on our approach path gently slowing as we get lower. We cross through 30 feet AGL at 30 knots. As ETL is passed through (about 10-15 feet AGL) power is pulled in to arrest the descent rate. After power is pulled in, there is a gentle forward move to walk to the spot.

 

The idea of this approach is to stay out of the gray area of the height velocity chart as long as possible. Also, to carry ETL as low as possible, in case a running landing is necessary.

 

 

Alright, that is pretty much it. Let me know which of the two you like better, and why. I appreciate your help with this one! I hope this will give you all something to think about, and generate a decent debate (pun intended).

 

Dave

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Of the two I like #2 better - You're in a high power, high DA situation, if you should happen to suck a valve you're in trouble with the first approach. I would probably extend the downwind for a longer final and shoot as shallow an approach as I could get away with given the terrain. I'd also try to hit ETL at about a 2 foot skid height since you imply there's room for a running landing. That way if I've miscalculated my available power I'm set up to settle comfortably with a short run out.

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if I had to pick one I would say #2 given the 300c and the senario. I agree with pogue.... if you're limited by density altitude or power etc... a shallow approach would be best (if you have the room at the landing area)... bring it in low and stay 20kts til at least 5 feet then slow it up and terminate in a low hover.... that way if it continues to settle you're already there with a light touchdown

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Either approach could be appropriate, depending on what you are trying to accomplish with the approach. If you are simply flying an approach to a spot for landing (not training) you should use the lowest power method you are familiar with, and is suitable for that landing spot. If this answer sounds a bit cryptic, it is. My point is that neither approach is wrong, and neither is right. You have to use ADM to determine which you should use. If the flight is a training flight, why not teach both (not at the same time) so that the student is able to make that decision when faced with those conditions in real life. I am not saying you should perform an approach that could be dangerous in those high DA conditions, but that you should teach multiple techniques in a safe manner.

 

On a side note, if you need to pull full throttle to terminate either of those approaches, without an excessive descent rate, at 6400 DA in a C model, you might consider having your mechanic check the engine. Doubly so if you have to use full throttle to hover into the wind. If there is nothing wrong with the engine, then your descent is probably too fast. In our C models, at those DAs, we will typically pull 22 inches of manifold pressure to hover at 3 feet into a wind less than 8 knots. Normally there is about 1-2 inches of excess power.

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There is so little power required when descending, I think its easy to slow down too much, too fast. I prefer to be at 30 feet doing 60 knots over the numbers and then bleed down the airspeed to a low hover. Remember the ol deadmens curve? We ( at least I) don't climb more than 10 feet until I hit 55 or 60 knots on take offs....so the same in reverse. I know if I fly at 45 knots I will be giving up some altitude to get to 60 in case of an auto...I like seeing 60KIAS, it keeps me warm and tingly at night ..and I try to never get below that unless I have a lot of air under me. ( r22 flying, R44 is even faster)

 

Steep or confined approaches may be a totally different story, but normal to the runway I like it fast...burns a lot of runway, but thats what its there for.

Edited by Goldy
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The type of approach, as well as takeoff, that I use depends on the approach or takeoff area. If you have a mile or two of runway, then you can do almost any type approach you want. If you're landing to a confined area, then it's another story. I generally prefer a slow approach, using about 200-300 fpm descent, keeping that descent rate throughout the approach. I may start with a higher descent rate, but the final 300 feet or so will almost always be that slow, maybe slower, depending on the situation. At night, and into an unprepared LZ with possible (probable) wires, I'll probably be even slower. Going to a runway, it doesn't make a lot of difference.

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Here is what I do, we normaly fly our 300c at 8000 -9000 foot density altitude. Slow the helicopter down to an apparent brisk walk using your perphial vision and ride the the shutter of ETL ride that shutter till you are about 10 feet off of the ground if you have your power in early enough and have shot the approach right you won't have to add any more power at the bottom. If you shoot fast approaches you might not have enough power at the bottom to arrest the rate of decent. Most importantly keep your head up not on the instruments and get the power in early. Just my opinion but it works for me day in and day out.

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