Monday, April 8, 2013

Hello Dolly!

 After a smooth scene flight yesterday, I flew my crew from Palm Beach back to the Martin County Fire Rescue hangar at the Stuart, FL Airport; where I am filling in this week.

We enjoyed the scenery coming up the coast, and were cleared to land upon initial contact with the tower. As I eased the aircraft toward the landing dolly (a wheeled platform used to move skid-gear helicopters into and out of hangars),I spoke into the microphone, "it's all over now but the dolly landing." I then set about relaxing for the task at hand.

One of the crewmember's said, "oh, yeah, the good old dolly.  Both of them mentioned that they would be happy to have me land on the cement and let them out before the airshow, if there was going to be one.  

Dolly landings have vexed more than one pilot, and led to some spectacular crashes. 

This gentleman fell prey to the hazardous attitude known as "impulsivity", or the overwhelming urge, when faced with a challenging situation, to do something right now. Action without thought, especially when distracted or upset, often makes a bad situation worse. It's much better to hold-up, stop, and think.

He bounced laterally, and got one skid on the ground, he was probably upset and embarrassed, (I would be too) and felt the need for an immediate corrective response. Imagine though, if he had simply stopped at that point, with the aircraft half on and half off the dolly...

I scared myself silly 15 years ago while performing a power check in a BK at the Geisinger Medical Center in Danville PA. I had the stupid idea that I could perform this check - in which the aircraft is brought light on it's skids using power from one motor at a time and instrument parameters are recorded - by myself; without bothering to reposition to the soft, forgiving sod. So I was the sod when, just as I was writing the turbine temperature on a notepad, my BK decided that the rotor torque-to-tailrotor thrust ratio was unbalanced and the friction between skids and wood planks was nil. The aircraft jerked in the yaw axis and shifted on the platform, which had become suddenly and alarmingly small. I dropped the pen and pushed down on the collective to stop the motion, and luckily did not fall off the dolly in a 4 million dollar helicopter.

Some operators refuse to use dollies, citing the risks involved. (sometimes they are simply undercapitalized, and don't worry about what the crews have to put up with) In any case, using a dolly does entail risk. There are also benefits however. A dolly is the fastest and easiest method of moving a skid-gear helicopter into and out of the safety of a hangar. One would think that someone in charge of a multi-million dollar asset would think enough of it to arrange for a multi-thousand dollar enclosure by way of protecting said asset, but that isn't always the case.

In an area where thunderstorms can explode into existance in a matter of minutes, a dolly allows a crew to keep an aircraft safe, while remaining ready to respond at a moments notice. Without a dolly, a crew must mount ground handling wheels and push (or tug), and this too is risky business. People pinch fingers, pull muscles, damage skid tubes, lose control of rolling aircraft, and learn quickly the gradient of the ground underfoot.

Another option is a wheeled cradle, which must be manouvered underneath the belly of the aircraft and positioned either on lifting points or spots on the cross tubes. A cradle can punch a whole in the belly, break off antennae or lights, and damage the surfaces it contacts.

The thing to keep in mind is that if it is a pain in the butt to move a helicopter, it will get moved less, and may get left outside when it should be inside, or inside when it should be outside (which delays response times).

A story about cradles...

About six years ago, I got myself sent up to Sioux Falls SD to fill in at the Avera-Mckinnon CareFlight program. At the time, they left their Bell 222UT sitting outside on a rooftop helipad in all but the worst weather. South Dakota produces lots of "worst weather." When storms and freezing precipitation would draw near, it was up to the lone pilot to fly the aircraft to a leased hangar space at the local airport for safe keeping. Unfortunately, this program didn't ascribe to the benefits of a dolly, so a battery operated cradle was the aircraft-mover of choice. And it can be done with one person, right? One night, I fly over to the hangar and land out in front. I open the door, survey the piece of concrete saved for my ship, and motor the little cradle out to the deuce. There is a slight gradient down and away from the hangar entrance, and a light skim of frost on the asphalt, but I get the cradle positioned properly underneath, walk around two or three times to make absolutely sure I am not going to lift metal into belly, and ease her up off the ground. So far so good. Next I begin to push her backwards into the hangar, turning as I go. The tail swings into the open area, I begin to straighten up, and we hit the incline. The cold batteries driving the hydraulic wheel-motors begin to fall short, the little motors whine down, and then it happens.

The entire aircraft, at a slight angle and on a slight incline, begins to slide sideways. There are other aircraft nearby.

This is what is known in aviation parlance as an OH CRAP! moment. There is nothing I can do but watch it unfold. She slips a foot or so and stops. Luckily, there is no aircraft to aircraft contact. When my lungs can again take in air, I utter "Thank f-ing GOD." (I know, I should not have said that, but it just came out)

So, as I said, dollies entail risk, but cradles do to, and so do ground handling wheels. There is no free lunch when it comes to ground-handling an aircraft.

One noteworthy fact about dollies and pilots is our desire to land straight on them. Pilots take it as a point of pride that the aircraft will end up centered on the dolly, and pointed straight ahead. Perhaps they should not. If the aircraft is reasonably centered, all of the skids are on deck, and tipping off is not an issue, perhaps we should stop right there. I landed a bit crooked on the dolly here in Stuart a couple of nights ago, and my opposite pilot, by way of helping a brother out, managed to make the aircraft look straight in the hangar by turning the dolly a few degrees. 

So why worry about moving once down? Because it is during this repositioning of a safely landed aircraft that we risk damaging the aircraft.

When I was fresh out of Fort Rucker, in 1986, I went straight into the CH-47 transition. My stick-buddy was an older National Guard pilot, a cool guy, and a good "stick." His full-time job was lead pilot for Colgate-Palmolive, flying a BK-117 for executive transport. He told me about the pilots that worked with him. He laughed about how hard it was for one guy to land on a dolly and made it clear that landing straight on the dolly was a criteria for a good pilot.

A couple of years later, I heard about this BK-117 losing it's entire tail rotor, gear box, and fin, shortly after departing from the downtown heliport in New York City. 

During my BK transition in 1999, the accident was brought up when we studied the doublers (an extra layer of metal skin) at the fin-to-tailboom attachment point. I correlated the extra strengthening to the Colgate crash, but didn't correlate one essential bit of information that was key to the mishap.

 It wasn't until  2012, when I met an EC-135 check airman named Art while getting checked out in that aircraft.  During ground school, we discussed the reinforcing structure at the aft end of the 135's tailboom, where the fenestron (the fan-in-the-fin) attaches to the tailboom. I brought up the Colgate crash, and the need for doublers. Art exclaimed, "I know about that." Art told me that Colgate's lead pilot, my stick buddy from Rucker, insisted that his pilots land straight and centered on the dolly, and those pilots did their best to please him....

When I land at an angle, or off center on a dolly, and I want to fix the problem, I have some choices. I can take back off to a hover, back up and try again; or I can bring in some power, get the aircraft light, and use the cyclic stick and pedals to effect movement on the deck.  Of course, the more lifting power I apply, the more apt I am to slide somewhere I don't want to go. Finally, I can use just a small bit of lifting power, and lots of tail rotor thrust, and lever the aircraft straight. Unfortunately, helicopters aren't designed for such forces to be applied to the tail while sitting on the ground. That tail rotor is out on a long arm, and the forces are magnified - this is why we can crank it around while still in firm contact. This cranking is what led to the failure of Colgate Palmolive's tail assembly.

So, when we get our aircraft down safely on a dolly, perhaps we should leave well enough alone.

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