Imagine (god forbid) those gears collapsing on landing
Gears where already down. According to your writing of events. So they have not been out of there locks. So how could they collapse.
theres a flap above the F/Os head that is used to lower rthe main gear rear doors for maintenance and daily checks. There is no mention of this in the checklist for gear problems.
Start studying again "Dash&Thump".
Behind this flap, as you call it, is the emergency gear extension handle. Read the folowing:
Alternate Extension Sequence:
Main Gear:
1. Opening Ceiling Alternate Release Door ==> Moves Bypass Valve==> All Actuators At Return Hydraulic Pressure
2. Moving Inhibit Switch ==> To Inhibit ==> Prevent Selector Valve From Opening ==> Blocks #2 Hydraulic Pressure
3. Pulling Main Gear T-Handle ==> Releases Uplocks of the MAIN landing gears And the Forward And Center Doors locks ==> Main Gear Extends Partially By Gravity
4. Use Hand Pump ==> Completes Main Gear Extension Through Its Own Actuator
After that almost the same procedure with the nosewheel.