Off Airport Landings

Back in August I got to do what was supposed to be a long loop hike in the mountains up on the Idaho-Montana panhandle. Ended up cutting the hike short because of worsening weather, but got to see something that you probably won’t ever see in a helicopter, but will help your pinnacle and confined landings. The zone of demarcation is the transition layer between the smooth (laminar) flow over the terrain, and the underlying turbulent layer. Stay above the ZoD and your ride will be smoother and power requirements lower. Get under it and you will be dealing with turbulence and down drafts. Just watch the video, and if anybody’s up for it, I’d like to hear some opinions on how you might be able to best do an approach to this saddle.


Zone of Demarcation

Cherry Drying Season

Spring is cherry season, which means all kinds of helicopters come into our area for cherry drying contracts. This year, I was fortunate enough to know one of the pilots working what turned out to be a pretty rainy season. Luck wasn’t all working for me though–I had a 1-week business trip and had scheduled my BFR right in the wettest period. I ended up with just 0.8 hrs actually flying the contract with him, but got to see him work a couple of fields from the ground as well as from the air.


Yeah, he’s doing it in an R22. I watched a UH-1 do the same field a few years ago, and it seemed like he was 50-75 feet up. In contrast, the R22 was right down on top of the trees. Once the R22 is low enough, the force of the downwash is the same though–it looks like the trees are going to lay over flat when you’re right over the top of them.

On the flight that I did with him, we covered what seemed to me to be a nightmare scenario. Lots of farmers out here have small cherry orchards–one of the reasons why you need to find a cherry contract is because those contracts serve lots of small plots. It’s not uncommon to find a house in the middle of an orchard which brings all the other obstructions. Rows of trees to break the high winds border many orchards, and there are usually wind turbines spread throughout for frost control during the cold desert evenings in the spring. This field had all those obstructions, plus an unusual layout, power lines running at an angle through the middle, uneven terrain, and a few birdhouses just for fun. It’s unnerving enough to be hovering so high (even though we were only a few feet off the tops of the trees) and in gusty conditions. Being surrounded on all sides by obstructions–and having to maneuver close enough to them to dry the trees below them–added to the fun. Just keeping track of what to look out for was beyond my ability, and I was content to watch this 1000+ hour pilot do his work.

Thoughts on Pinnacle Landings

I had the chance to fly some last weekend, and took the opportunity to do a few pinnacle landings. The pilot who I was with has just a little more helicopter experience than I do, and quite a bit of fixed wing time. He’s done more of what I’d characterize as “real-world” flying (ie, out of the flight training pattern), and his experience shows. We picked a reconned a pinnacle just south of the airport: a nice ridge with a steep drop-off on the west face, and a smooth slope moving off to the east. The wind was blowing briskly up the face at probably 12-18 knots.

Wind is one of the factors that dictates how you approach a pinnacle. When the wind is light, the airflow is laminar (flows smoothly over the earth, following its contours). As the wind picks up, two zones that are separated by a “demarcation line” form. Above the demarcation line airflow remains laminar and smooth–good for flying in. Below the demarcation line, turbulence and eddies are going to toss the helicopter around. The method you’ll read about in the FAA Rotorcraft Flying Manual uses a steep approach that terminates right at the windward edge of the landing zone (LZ). Flying a steep approach keeps the helicopter above the demarcation line and in the smooth air. The downside of the steep approach is that it gives you fewer options in the case of trouble and, especially if you don’t plan it well, can require larger power changes. Also, as the wind picks up, your approach has to become increasingly steeper to stay above the demarcation line.

The alternative to flying a steep approach is to use a shallow approach. I’ll add a disclaimer right here that you shouldn’t try anything I’m suggesting–find an instructor who knows what he’s doing and have him show you. A shallow approach offers a few benefits that I might elaborate on at some point, but one key advantage is that you fly the approach so you don’t have to fool with trying to stay above turbulent air behind the LZ. In this instance, we could fly the helicopter along the face of the ridgeline, taking advantage of updrafts there while keeping a convenient escape route down the face. So here’s how I [tried to] fly it. Both my high and low recons were elongated ovals, with the high recon passing just over and to the east of the knob that we were going to land on. On the low recon, I descended to just above the LZ, flying the helicopter parallel to the face of the ridgeline. The final approach phase was right along the cusp of the of the pinnacle face. The entire approach is lower, and it’s set up to be a shallow descent that terminates right at the LZ. One key feature of flying this approach is that you start with the wind perpendicular to your flight path. As you slow, you still need to align with the wind to stay in trim, so you are moving along the ridgeline laterally as you approach the LZ. Since you never move behind the LZ, the helicopter never enters the turbulent airflow there.

For the record, I haven’t flown much in the last 6 months, and the Schweizer 269A is still a strange helicopter to me (different sight picture, higher skid height, no governor). The results weren’t as nice as I’d planned it in my mind: mostly, I flew it too low and started the approach too soon, so that I ended up moving over the ground sideways and lower for a lot longer than I’d have liked. In theory though, flying the approach like this has it’s benefits–for example, we were above ETL throughout the approach, right up until the point where we came to a hover.

The other pilot took the helicopter and demonstrated how he would have flown it. Not only did he execute his plan much better than I did mine, but his approach had some advantages that I hadn’t considered. Basically it was a hybrid between the steep and shallow approach techniques. He flew the approach pattern the same as I did, but a bit higher. As he lined up on final, he started a shallow descent as if he was shooting past the LZ. Once he intercepted a steep approach sight picture though, he flew that profile to the LZ. The steep portion was about what you’d do at the termination of a quick stop…or maybe about how you’d fly into a confined. His result was exactly the same, but kept us up at a much more comfortable altitude until the very end of the approach. That extra altitude makes it easier to exercise the option of breaking off the approach and flying down and away from the pinnacle face. One of his (well-justified) complaints with my approach was the risk of catching a skid while moving laterally along the face of the pinnacle–even if I’d flown it at the altitude I wanted to, I was still lower for a longer portion of the approach…my approach looked a lot like what a shallow approach to a runway would look like. Some unlucky combination of a change in wind, the lateral flight path, and an unseen obstruction would have ended my approach very badly.

Off-airport landings are something I think a lot about since confined and pinnacle landings are the mission profile for many helicopter operations. No two are the same, and getting your head wrapped around off-airport landings is tough to do in 200 hrs. Even though I’ve read up on different methods, taken a mountain flying ground course, and spent a good bit of time during my training to try different techniques, I recognize that I still have tons to learn. I’m in no position to be saying what the optimal approach is, but I liked the shallow-to-steep method.