On my TB20 a new sudden annoying electrical noise/ Interference is coming via radio/headset when the gear lever is set down for landing in the first seconds of the gear down process. This seems to occur when the electrohydraulicnpump is starting to run in the first few seconds. The gear comes down without any issues.
Who has an idea where these interferences come from and how to eleminate?
First check the pump has a good earth ( ground ). Problems like this are usually the simple stuff but whatever it is make sure the landing gear is lubricated properly as this is the usual reason the gear will fail to free fall if the pump fails and the noise is probably the gear system trying to tell you something.
Well, the aircraft just came out of the annual inspection and got e.g. new passive struts for the front wheel and the main gear „looks“ lubricated, however. Maybe more can only be identified on jacks.
Radio interference from electric motors comes from sparking in the brushes, and is usually strong when starting but fades away as the motor picks up speed. If it did not happen before, it may be a sign that your brushes are worn.
Ok, thanks. In the case of worn brushes this is pointing finally to a new pump or OH pump. I‘m wondering if this could be the case after 1.600 hrs? Maybe it‘s time to consider that.
The TB20 is not an aircraft I have had much to do with but the basic landing gear system is similar to that fitted to Piper & Rockwell aircraft, the suggestion from Ulitranomad that it might be a problem with the Brushes in the motor is a good one.
I have seen piper aircraft that have not seen any grease for years in the difficult to get at greasing points simply because the hangar rat to who all the dirty jobs fall has not been told the location or is too lazy to do the job properly.
The result is a stiff gear that works OK while under hydraulic power but if required to free fall will not engage the geometric locks. The result is a gear collapse on landing. This is why my first action if a gear problem is to assure the free fall system works, at least then if the hydraulics fail the aircraft will land without further drama.
I was once charged with investing why a PA28R gear collapsed on landing after a free fall gear extension, the reason was the ( difficult to access ) trunnion bearings had not seen grease in years, a quick application of the grease gun solved the gear problem …….. but not the damaged wingtip.
Jacked up it during the annual the freefall worked, but well, one never knows if a correct diagnosis is found yet.
I think it is buggered brushes on the gear pump motor.
The gear pump – details here – and the rest of the system is the same as most other GA retracts. Even the little Lancair 320 etc uses the same parts.
Maybe there is a capacitor filter somewhere, which has become disconnected, but I doubt it.
Yes; greasing is essential, most maintainers don’t do it, but on the TB20 GT you have lots of grease nipples so you can do most of it very fast, even on a 50hr check.
Only the nose gear uses gas struts for extension; the main gear is hydraulically driven both ways.
I have an armature from a gear pump, which I believe is faulty, and I was going to send it to a motor repair shop for a rewind… any motor repair shop can do this, but of course don’t expect an EASA-1 
ok, Thanks. The brushes make sense. I´ll investigate hoping not to have too much downtime.
