lml@lancaironline.net Mailing List Archive

Lessons learned from my hydraulic landing gear pump failure/seizure and successful backup procedure gear extension: 1) If the hydraulic pump light comes on and stays on during normal flight, to avoid over eating the pump (see Bob’s caution below), pull the hydraulic pump circuit breaker until ready to lower the gear. 2) As current from the pump failure may cause the alternator circuit breaker to pop, reset the alternator circuit breaker if necessary after pulling the hydraulic pump circuit breaker. 3) If the gear will not lower with the normal procedure, follow the backup landing gear extension procedures: slow airplane to 120 kts., test gear lights, pull hydraulic pump circuit breaker, lower gear handle, activate accumulator or hand pump, yaw aircraft and increase positive Gs if necessary to get three green lights and land as soon as practical even if you don’t have three green lights. 4) Replace the gas strut to the nose gear annually. 5) Practice the emergency gear extension procedures in flight which will verify the system, including the gas strut, is working properly. 6) Review all emergency procedures regularly, and 7) Annually train with a LOBO approved or like instructor.

Shane Bangerter

89GG IVP 320 hrs.

From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of William A. Hogarty
Sent: Monday, March 10, 2014 10:41 AM
To: Lancair Mailing List
Subject: [LML] Re: IV-P Landing Gear

Bob:

Nice article on the IV landing gear operation.

I would like to stress the importance of the monthly inflight check of the system and the necessity of replacing the nose gear gas actuator during each annual. (don't rely on a ground retraction test)

If you have an electrical failure, the gear will drop as you point out BUT if the nose gear gas actuator is not fully pressurized (100 psi), the nose gear will appear down but there is a strong possibility that the linkage does not go overcenter and lock. Without electrical power, you will not have your gear indicator lights to warn you. (don't ask how I know)

Keep up the good work.

Best regards, Bill Hogarty

On Mon, Mar 10, 2014 at 6:48 AM, Robert R Pastusek <rpastusek@htii.com> wrote:

Gentlemen,

Without reflecting on the cause of the most recent IV-P loss, I was asked to review the operating principles of the Lancair IV landing gear system for those of you that did not build your airplane. Hopefully this knowledge will help you if you should have difficulty with the landing gear--which, by the way, has a different operating principle from the Legacy and 3-series aircraft.

The landing gear in the IV-P is hydraulically operated by an electric power pack (a pump/reservoir assembly commonly used to control boat lift/tilt out-drives). Hydraulic fluid is circulated from the pump to a gear/flap control on the center vertical instrument console in the cabin. The gear handle is actually a hydraulic valve that switches fluid flow between the “up” and “down” sides of hydraulic actuators that are attached to the two mains and the nose gear.

With the landing gear handle in the UP position and the hydraulic system pressurized, all three gear are retracted and held up by the pressure. There are no up-latches. If you lose hydraulic pressure in the system for any reason, the mains will “free-fall” to a partially-extended “trailing” position but will not fully extend because they must move forward (against an air load) to do so. NO AMOUNT of maneuvering, touch and go, or flying around will fully extend the mains, and they WILL fold back into the gear bays at touchdown if partially extended. No exceptions. The only way to fully extend the gear is to apply hydraulic pressure to them, either by restoring the electrical pump to normal operation, or by use of the hand pump between the front seats to manually pump fluid into the main gear actuators. There are several things that need to work correctly for this to happen, so emergency gear extension--both on jacks and in-flight-- should be one of your required condition inspection items.

The nose gear is equipped with an air spring that causes it to extend fully if hydraulic pressure is lost. Once extended, it can only be retracted by restoring normal hydraulic pressure with the gear handle in the up position. The emergency pump applies pressure only to the down side of the main actuators; it does not supply fluid to the nose gear actuator in any circumstance. So to repeat, with a loss of hydraulic pressure, you’ll get an “automatic” nose gear fully extended, and “trailing” mains. The hand pump should be able to fully extend the mains, allowing them to lock down automatically, but if it doesn’t, the mains WILL retract on landing. There are no known alternatives or exceptions. By the way, if you can get the mains fully extended (green down lights), the actuators have built-in locks that should hold them fully extended, even if hydraulic pressure to the actuators is subsequently lost. Even so, if one or both of the main gear indicator lights should go out, consider a final tug on the emergency pump just before landing. If it can be pumped, do so; if it doesn’t move, you should still have fully extended mains.

For me, any un-commanded extension of the landing gear would be time to put the airplane on the ground and sort out the electrical and/or hydraulic problem--for several reasons. As an example, a hydraulic leak can dump all the fluid overboard quickly, and allow the pump to run continuously. In time, it will destroy itself, and has been known to catch fire--it’s not designed for continuous operation.

One other thought. Flying by the tower, or even having another airplane look you over for extended gear is probably a waste of time, and may give you a false sense of security. Unless the observer is familiar with the IV landing gear system, he/she is unlikely to identify the difference between mains that are fully extended forward and those in the trail position. They will note that the nose gear looks good (it should be), conclude that the mains are also “extended,” and report that.

Lastly, the gear handle has an electro/mechanical “lock” built into it that SHOULD prevent it being moved out of the down position when the airspeed is below about 90 Kts (this is adjustable, so it could be more or less). If you move the handle to UP when the airplane is on the ground and the hydraulic system is pressurized, the weight of the aircraft SHOULD prevent the mains from retracting, but the nose gear will definitely retract, dumping the nose and prop on the ground. Your checklist does require you to check that the gear lever is in the down position before applying power to the aircraft, doesn’t it?

Landing gear malfunctions are serious, and can result in major damage to your airplane even in the best of circumstances. They should not, however, kill or injure you or your passengers if you apply your training and keep your cool. Lancairs fly well in any known landing gear configuration. So task #1 is always to fly the airplane to the scene of the crash…always.

I’d be pleased to talk to any of you either on- or off-line about this. Just drop me a note.

Bob Pastusek