Tinkering with the C172RG Gear Pump Circuit Breaker flying circuits ..... this is what may happen
Anecdotal evidence as follows.
FI (=CFI) is conducting flight training to a candidate-FI on the C172RG doing circuits. After some circuits flown, after rotation the FI pulls the Gear Pump Circuit Breaker. Student: "What are you doing?". FI: "That's my business, you fly the aircraft, keep operating the gear lever per checklist as before". Now after selecting gear up the green light remains on, no red transition light shown. Several more circuits are flown. In the debrief student ask "what was that with the CB?". FI grumbles: "The RG is prone to gear-mechanism wear, we must not do too many circuits in sequence".
Later, with the student now become an FI, and having performed instruction several weeks on C152 and C172, a lesson is scheduled on the C172RG, the lesson detail is circuits. With two circuits completed the FI pulls the Gear Pump CB and tells the student to keep operating the gear lever per checklist as before. And on climbouts to action and call out "gear up, no lights", on every downwind to action and call out "gear down, green light", imagining the gear lights to go off and the green light to come back on, ignoring the green light remaining on continuously. The practice is explained as a compromise limiting gear-mechanism wear while following the checklist as much as possible. On the next final "green light" is observed and called out. Touch-down is made properly on the mainwheels first, then comes down the nose. The nose keeps going down until chin on the runway and the aircraft comes to a grinding halt, then silence .... The gear lever is down, the green light is out.
I am the FI. When I see the CFI the next day he tells me "I should have told you to push the circuit breaker back in before every landing".
The aircraft is jacked up in the hangar and present are maintenance personnel, investigation commision, and myself. Several tests are performed. With gear retracted, the circuit breaker pulled, green light on, the mainwheels are being hit from below simulating some of the dynamics of the landing, and the nose wheel downlock releases, green light comes off. The C172RG apparently needs the oil pressure to secure the downlock.
With a manual gear extension you manually pump the gear down, forward into the airstream then slightly up until the stop, so the pressure is there. POH says whenever the gear pump fails to cut out you must pull the GP CB, but insists it being pushed in prior to landing.
I have since then refrained from tinkering with the gear pump circuit breaker flying circuits.
jr