Do you fly a Factory Built Gyroplane? If so you may be aware of the 5 year rubber component replacement on your Rotax engine and possibly airframe. It appears that a number of airframes and engines have had the rubber components replaced with Silicon based items to remove the 5yr requirement from the maintenance schedule. A good idea in theory. However, there is no approval for this modification or substitution of components in place for any of the FB-gyros in the UK. Here's how I interpret the regulation for CAA Permit Aircraft. The photo shows silicon hoses fitted to a Cavalon. The rubber hoses on the engine have been swapped for silicon based items and like-wise the hoses for the cooling system. The sad thing here is that yes the Rotax components needed changing - for replacement Rotax parts - but the coolant hoses to the radiator and airframe did not necessarily need replacing as these could be run "on condition". Both Magni (who do use silicon hoses) and Auto-Gyro made provision for this many years ago. All the non-standard items will need to be removed and replaced with approved components. These approved components can then be run "on condition" when the time comes. Unapproved components can NEVER be run "on condition" as they cannot comply this the aircraft manufacturers statement of acceptance to run "on condition". For example Auto-Gyros' running on condition Service Bulletin SB-135 only applies if Rotax or Auto-Gyro supplied parts are fitted, the inspector/engineer can then determine whether to keep or change the components. The inspector/engineer does not have the authority to declare that the engine is running "on condition" and then fit whatever components they choose. They could, however, apply to the CAA for Mod. There were no approved Mods on this subject known to the CAA on 20/09/21. I am not aware of any having been granted since. Currently the LAA does not grant Mods for FB-gyros and their line is and I quote; "I'm afraid the rubber/silicone hose issue is not yet resolved. Until advised otherwise, Yes, owners should (must) fit factory supplied parts." KC 31/01/22 Take note the statement above could affect your permit renewal application or even your current permit.