Note: This question is a bit odd and the feedback is unconfirmed currently, but there is a "most correct" answer here in our opinion. Please do let us know if you see this question in the real exam and anything you can remember about it, thank you.

Learning Objective 021.04.01.02.06: Describe the various protection devices to avoid inadvertent gear retraction on the ground and explain the implications of taking off with one or more protection devices in place: ground lock (pins); protection devices in the gear retraction mechanism.

Let's go through the options:

• "Insert the ground lock pins."
  • Correct. Ground lock pins are for the landing gear when an aircraft has a retractable undercarriage, and they slot into the gear downlock system to make sure that the gear cannot retract whilst on the ground, no matter what happens to the hydraulics or external conditions. For long term storage, they must be fitted. They are part of the pilot's checks before flight, also, as leaving them in will not allow the landing gear to be raised.
• "Leave the parking brakes on."
  • Incorrect. The parking brakes of an aircraft are just sealed off hydraulic fluid, and leaving them on for extended periods of time can lead to seizing of the brakes, or potentially a leak of the hydraulic fluid through small imperfections in the system, allowing the brakes to gradually release. Aircraft are chocked or tied down for long term storage.
• "Leave the flaps in the extended position to release the hydraulic pressure."
  • Incorrect. Flaps should be up for long term storage, to avoid wind damage, damage to the mechanism, keep birds from nesting in the flap tracks, etc. The hydraulic pressure has nothing to do with it.
• "Always park the aircraft facing upwind."
  • Whilst this is best practice, it cannot always be done, and even if you park into wind one day, for long periods of parking, the wind will change and the aircraft will no longer be into wind all the time.