Definition
Rib thread is the reinforced cord or lacing material used to attach fabric covering to the ribs of a fabric-covered aircraft wing or control surface, securing the fabric tightly against each rib so it cannot lift away in flight.
Plain English
A strong thread used to tie the fabric skin of an aircraft down onto each wing rib so the fabric stays put when the aircraft is flying.
Context Anchor
Seen in fabric-covering installation, repair, and inspection on fabric-covered wings and control surfaces.
Derivation
‘Rib’ refers to the spanwise structural members of the wing that give it shape, similar to the ribs of a body that hold the chest wall in place. ‘Thread’ is the cord doing the tying. So the name simply describes what the material does: thread used at the ribs.
Why Pilots Care
If the rib thread fails or is improperly tied, the fabric can lift, balloon, or tear in flight, changing the shape of the wing and degrading lift, control, and structural integrity. Rib lacing is an inspection item on fabric aircraft.
Intuition Check
Do not read thread here as screw threads or a light household sewing thread. In this context, rib thread means strong lacing cord used to hold aircraft fabric to a structural rib.
Example Sentence 1
After covering the wing with new fabric, the technician used rib thread to lace the fabric to each rib at the spacing called out in the manufacturer’s manual.
Example Sentence 2
Inspect the rib thread for fraying or loose knots during the annual fabric condition check.