Airworthiness Directives; Learjet Inc. Model 45 Airplanes

We are adopting a new airworthiness directive (AD) for the products listed above. This AD requires replacing aluminum fire extinguisher discharge tubes with new, improved tubes; checking the fire extinguisher container for certain serial numbers; replacing fire extinguisher containers that have affected serial numbers; inspecting the pressure indicator on certain fire extinguisher containers for discrepancies; and performing corrective action if necessary. This AD was prompted by a report of accidental discharge of a fire extinguisher container and damage to an aluminum discharge tube. Investigation revealed that following the discharge an inaccurate pressure indication, due to the indicator dial being incorrectly staked, showed that the container was fully charged. We are issuing this AD to prevent inaccurate pressure readings and subsequent damage to the discharge tubes during operation, which could result in failure of the fire extinguisher system and an uncontained fire in an emergency situation.