The Civil Aviation Safety Authority of Australia (Casa) has begun the process of permanently shutting down Barrier Aviation, a charter company whose operations the regulator suspended last December. A Casa spokesman said the agency permanently grounded the company’s 34 aircraft because management ordered pilots to fly aircraft that were not airworthy. Casa also said Barrier, which operated a mix of Cessna and Piper light aircraft, never demonstrated a workable plan to address a variety of maintenance concerns.