This edition’s ILAHFFT is taken from our US equivalent organisation’s  NASA Aviation Safety Reporting System (ASRS) Callback Newsletter Issue 521 and is a cautionary tale about the need to conduct thorough pre-flight external checks, especially after an aircraft has been undergoing maintenance – ‘remove before flight’ flags are a great aid to spotting things that shouldn’t be there, but the absence of a flag (or a really grubby one that is hiding amongst grease/oil/dirt) isn’t fail-safe and doesn’t necessarily mean that all is well…

Hidden in Plain Sight – an item barely visible was missed on this B777 walkaround inspection and resulted in an expensive air turnback.

After landing at ZZZ, we tail-swapped into an aircraft coming out of the paint shop. We discussed the need for a thorough pre-flight, paying note to the static ports, pitot tubes, etc., and I as FO conducted the exterior and supernumerary area pre-flight. The weather was broken clouds and daylight hours. After take-off, we raised the gear and soon received a GEAR DISAGREE EICAS message due to left main landing gear disagreement. We notified ATC, levelled at 10,000 feet, and maintained airspeed at 250 knots. We completed the non-normal checklist for gear disagree. We contacted Dispatch, and they recommended we return to ZZZ. On [downwind]… we lowered the gear and received a normal gear down indication, landing without incident.

Once parked, Maintenance inspected the left main and found one gear-pin installed without a gear-pin flag attached to it… Maintenance informed us that four of their maintenance team had each conducted individual walkarounds, and none of the four who inspected the aircraft noticed the gear-pin was still installed. Four local Maintenance personnel had inspected the aircraft individually. They annotated in the Airworthiness Release Document (ARD) that they had pulled and stowed all the gear-pins. I, as FO, had walked around the aircraft and did not observe the pin still installed. It appears that there may not have been a gear-pin flag attached to the gear-pin,…making the pin challenging to see. The aircraft came out of a non-Company facility after significant work. All walkarounds require a thorough inspection; however, out of a non-Company city, it’s fair to say extra diligence is required. Additionally,…instead of looking for pins and flags, it would be better to look for an empty gear-pin hole.