All the Trimmings

or - "Why I don't like flying with Dave!"

Part I


Bill "Wingnut" Sherwood

In the middle of winter one night I was taking a Metro from Bankstown airport in Sydney up to Archerfield airport in Brisbane. I had a tonne and a half of freight on board, and a friend of mine named Dave. Dave worked for the same company, and was hitching a lift with me to get back to Brisbane. The weather down south was almost monsoon like, and it'd been raining for seemingly week’s non-stop so the plane, freight, and myself were far too wet for comfort. At least it was dry in Brissy.

In the middle of winter, there is a very strong northerly wind component, and so it often pays to go northbound at a lower level than what you normally would to keep below the strong headwinds – Even though the turbo-prop powered Metro runs far more efficiently at higher altitudes. I chose to head north at Flight Level 130, or 13,000' that night, and on the OAT (Outside Air Temperature) gauge it was a brisk -5°C, so I had to be careful of the wings icing up for the first hundred miles or so, until clear of the weather. The Brisbane area was as clear as a bell, and so to try to save fuel I started the descent as late as possible, so I could 'idle' the engines to minimise the fuel burn. Dave had slept through the entire trip, and was showing no signs of waking up, so I let him sleep while he could. He never seems to get enough.

The control column would not move at all!

 The elevators were jammed solid, and although I could still move the control wheel left and right to bank the plane, the pole was rock-solid in the up & down direction. I had set the plane up for a 4,000ft per minute descent - Normal for the sorts of descents that I do - So I had at least three minutes to fix the problem. A quick blast on the elevator trim confirmed that the pitch attitude could be controlled fast enough to slow the descent to about 1000ft/min.

After another minute or so of experimentation, I found that I could make the plane pitch quite accurately, and so I started to think about diverting to Brisbane International Airport where the runway is over 3500 metres long. I reckoned that I could set the plane up on a long approach and then gradually trim it onto the ground if I had to. It wasn't a pleasant prospect, but the only practical one.

It was then that I remembered reading an article a few years ago about a Kingair. The plane had a belly full of water and after half an hour or so at high altitude, the water in the belly iced up and 'froze' all of the control cables ....... I figured that this was the problem, so what I planned to do then was to descend down to about 2,000' and let the plane's airframe warm up, and so unfreeze the ice and release the control cables. I woke up Dave and told him what the problem was, and what I was going to do about it. He agreed, and didn't seem too concerned.

I contacted air traffic control for the Archerfield area and told them that I was going to be conducting 'aerial work' in the Archerfield area for about 15 minutes, and that I would contact them at the end of it. No worries so far, and no unnecessary alarm bells set off.

Whew! After about 2 minutes at 2,000', the elevators suddenly came free, so I started feeling pretty clever with myself, and finished off the approach into Archerfield without any more drama. Dave hopped out, had a big drag on a cigarette, then left shaking his head.

I had a look around the plane as best as I could, and out of most of the drain holes a thin stream of water was dribbling. Back patting time, I continued to think.

After an hour or so, the loaders finished doing their work, and so it was time to head back south to the soggy old Bankstown. I couldn't see any more water running from the plane - Which had a rather large puddle under it! So I hopped in and blasted off home.

I figured it'd be prudent to go back a few thousand feet lower this time, so as to stay below the freezing level ... Snuck into the circuit at Bankstown in the wee small hours of about 2:30am, and tried to be as quiet as possible during the approach and landing. Well, as quiet as one can be when the plane is as loud as a grid of racing cars! I left a big note for the next pilot that was going to fly the plane as to what had happened, and what my diagnosis was. (Patting myself on the back and feeling clever the whole time...)
Got a phone call the next day after I woken up - The pilot that had flown it at low level that day also had the same thing happen to him. SIX TIMES!!! Every time though, the 'lockup' disappeared in a few seconds. He flew it back to Bankstown, and I was due to fly it again that night on the same run. I grounded the plane until the problem was fixed.

The engineers pulled up all of the floorboards to try to find the problem, and a lucky thing they did, too. It turned out that the lowest part of the hull was almost bone dry, and so it was not possible that water had covered the cables and frozen them in place... All of the control cables were, however, very loose, so the first thought was that somewhere in the system was some slack getting caught up. Again, not so. (Although we found out that because of this the plane wasn't getting full 'up' elevator, or full aileron & rudder travel, so no harm at all was done by the inspection)

The real culprit was a gadget called the 'Stall Avoidance System', or SAS. The 'down' side of the elevator cables runs through the SAS, which consists of a round drum. When the SAS senses that the plane is approaching a stall, it activates an electric motor which turns the drum to pull the controls nose down, thus avoiding a stall. The clutch in the drum was jamming intermittently, and so stopping the elevator cable from moving! It could have jammed at any moment, but as fate would have it I had plenty of time to sort out what I thought the problem was and come up with some form of solution.

We were all very lucky that it decided not to jam during take off or landing.

Copied from the NZ Flanker sim group

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