Emergency Gear Extension
Beech 18 Emergency Landing System Gear Test
Testing the emergency landing gear extension system is an important part of the annual and 100 hour inspection for the Beech 18. The problem is that when you push the clutch pedal the gear will free fall out of the well and will slam down and the trolleys will hit the end of the slide tubes imparting heavy loads into the airframe and especially the landing gear system. The aircraft shudders under the violent action and it feels like it wants to come off of the jacks, which has actually happened. You are supposed to put several hundred pounds of sand bags or weights on the horizontal stab so the tail doesn't come flying up off of the jack.
The factory jack actually bolted to the airframe and would help eliminate the possibility of the aircraft bouncing off of the main jacks during this test but factory jacks are few and far between these days. With the various spar strap mods the original factory jack pads also have to be modified, or newly created, to clear the strap.
One way to avoid the violent action of this test is to run the gear a little aft of vertical and try the clutch at this point. The problem with this is it doesn't test the clutch under the full load of the weight of the gear. With the gear in the up position there is a heavy load on the clutch teeth hence the bang noise when the clutch finally releases. I think that it is important to test this system under the full weight of the gear to be sure that the clutch pedal, cable, conduit and cable clamp nut is in good enough shape to handle the load. Here is why:
I was checking a new owner out in his C-45H and while we were in the traffic pattern he put the gear handle in the down position when abeam the approach end of the runway. I noticed that there was no feeling through my seat of the gear cycling and the position indicators still said UP. I thought that this would be a good lesson to see if he noticed the gear was still up and I was delighted that he did. This Beech had the typical gear handle found in the ex military C-45H which is the large red clear plastic handle that lights up when in the gear is in transit. He recycled the handle and I noticed that the handle came to rest in an odd position. I tried the handle myself and the whole handle came off in my hand. I am pretty sure that this was not supposed to happen! I looked into the switch assembly to see if I could trip the gear down with my fingers but that was not going to happen. I then thought that this will also be a good lesson for my student to learn the actual emergency gear extension procedures.
We talked about the steps involved first and then I had him perform each step while he was flying the aircraft. First the control breaker for the gear was pulled. This is done so the motor will not try to move the gear against the manual system. Then the gear selector handle was to be put in the down position but this was going to be a little difficult with the handle now sitting on the cockpit floor. Next the clutch cover was raised and he was to be sure that the emergency gear/crank handle was clear so as to avoid any injuries. Then the clutch pedal was depressed. When he did this nothing happened, meaning the gear did not fall from the gear wells. Now things were getting interesting in deed. I removed the carpet from the access panel in the floor of the cockpit to gain access to the gear motor and clutch cable. Is your carpet glued to the cockpit floor? Did you know that there is supposed to be a hatch between the pilots and copilots seat for access to the landing gear and flap motor? Please be sure that you can access this panel in the floor of your Beech.
What I found under the panel was the conduit for the clutch cable had broken at some point in the past and so the mechanic had re routed the conduit around the gear box. This conduit is supposed to be secured in a hole in the casting of the gear box but this one bypassed the mounting hole. When the pedal was depressed the conduit simply flexed instead of pulling the clutch arm. I tried to move the clutch arm by hand but with all of the load on it it was not going to budge. I even tried to get my foot down there but this didn't work either. Luckily we had a tool box in the back so I was able to go and get a wrench to use as a lever. This worked and the gear was able to free fall toward the down position. My student cranked the gear the rest of the way out and the position indicators showed that they were down. With the lever removed the handle was rocked back and forth until the clutch teeth were reengaged. I did the forward stretch from the co pilots seat to look and see if the tire was visible at the junction of the nacelle and leading edge and it was. The third check is done by pulling the throttles back toward idle and no gear warning horn was heard. The rest of the flight was uneventful and the landing was normal.
This incident was an eye opener as it showed me the importance of testing the emergency gear system under load. Even if the conduit was sound this problem could still happen. If the clamp nut on the cable slipped, or the cable was improperly rigged
If the cable itself broke the same problem would present itself.
Imagine if one of us was flying solo and could not get to the tool box or otherwise reach some kind of pry bar like the wrench I found in the back of the airplane. This would have
ended in a belly landing and would have required new props, engine tear downs and a lot of sheet metal work.
One of the Navy aircraft that I bought years ago had a special tool in the cockpit. It was a forked type of pry bar tool that was made to solve the very problem that I encountered above. The tool even has a placard on it that shows how to use it. I guess that the Navy had encountered the same kind of problem enough that they made this tool and kept it near the pilots seat. I am presently fabricating this tool to install in all of our Beech's and I will make this available for others as well.
The need to do an emergency gear retraction at each annual is imperative but the violence and potential risk of damage associated with the procedure is a big deterrent. We recently decided to solve the problem and we believe that we found a procedure that works well.
We developed a method to test the emergency gear system that will not subject the aircraft to the harsh shock loads. I wanted to try and simulate the in flight wind forces on the gear which would normally keep the gear from hitting the stops. Many methods were suggested but what we built seems to be very simple, cheap to make, and works beautifully.
First we jack the aircraft up with three strong tripod jacks. Please don't use the cheap ones that look like they were made with bent up electrical conduit, buy or borrow some good and strong military jacks or their equivalent. Remember to make sure that the wheels are high enough off of the ground to clear as the main gear swings down and does an over center type of action during its cycle. Ground power is hooked up so the batteries will not be depleted. Our first cycle of the gear is just as the aircraft came in the door. Two to three cycles while watching each main and tail for any interference or rigging problems.
As a side note, I have heard owners/pilots say that they do not want to put too many cycles on the landing gear motor as it will wear out easily. The motor is strong and if properly maintained can last the lifetime of the aircraft. I have been flying rides in Beech 18's for 20+ years and I will sometimes make 20 engine starts, takeoff and landing cycles in a single day all throughout air show season and I have yet to change a landing gear motor on any of my Beech 18's.
Enough of my rant, back to the subject at hand.
The Process
Step One The the main gear doors are unbolted, usually at the rods, and they are held out of the way with bungees.
Step Two The gear is cycled again so we can see inside the wheel wells for any conflicts with hoses, spar straps and structure. With the gear left in the up position is at this point that the emergency gear system should be checked. If the owner is around I will have him in the cockpit to learn the procedure first hand.
Step Three We took two fifty pound sand bags and put them inside a plastic dairy type crate. We then placed the crate on top of a piece of carpet to increase the friction between the crate and the floor. The floor in our shop is painted so when the plastic crate overcomes the initial friction it tends to keep moving. The carpet helps to keep the crate from sliding too far.
Step Four A rope, about 8 feet long was secured to the crate. Make two of these; one for each main gear.
Step Five A strong 48 inch rubber bungee cord was looped around the axel on the side opposite of the brake caliper.
Step Six The S hooks on the bungee cord were replaced with a karabiners so they would not come unhooked.
Step Seven Each crate and sand bag apparatus is positioned aft of each landing gear leg.
Step Eight The gear is raised and the crate moved aft until there is slight tension on the rope and bungee.
Step Nine We use a piece of carpet under the crate to provide the correct amount of friction between the crate and the floor. The plastic crate would continue to slide too far without the additional friction.
The Finish Here is our finished product from the front. Make sure everything is free and clear of the crates, and there are no chocks beneath the gear.
Here is a high resolution video posted on YouTube of the system in operation:
It is imperative that after the gear has been manually cranked to the full down position that the clutch pedal is released and the emergency gear crank is rocked to be sure that the teeth of the clutch are engaged. Click here to see a video clip of what that looks like at the clutch. In this video the gear is cranked all the way down and then the clutch is re engaged but the position lights indicated that the gear was not fully down so the pedal was depressed again and the manual gear crank was turned in the opposite direction and engaged where the position lights indicated a safe gear condition.
After the emergency system check we will make any adjustments as necessary and will hook up the gear doors and cycle it several more times to be sure that everything is operating properly.
If you have any questions at all please call me (Taigh Ramey) at the shop number below and I will be happy to answer them.