The Aircraft Inst. & Development Inc. 548‑721 (part number 26T101‑2) is a trim indicator panel used on elevator and rudder controls to display pilot‑selected trim positions. Common failure modes for this type of indicator include loss of illumination due to burnt LEDs or relays, drift in the displayed position from misaligned potentiometers, and intermittent electrical contact at connector pins. First‑check diagnostics: verify power supply voltage to the panel, inspect all wiring harnesses and connector pins for corrosion or loose contacts, and confirm that the trim potentiometer is within spec by measuring resistance across its terminals. If the indicator remains unresponsive, review any associated error codes from the aircraft’s avionics system and replace the LED module or relay as needed.[oss-gpt-20b]