COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Hot Air Balloons AD/BAL/15 Amdt 1 Applicability: All hot air balloons. Altimeter Graduations 2/96 Requirement: (a) Check that the height scale of altimeters, installed in compliance with the operational requirement of Civil Aviation Orders Section 20.18, are graduated in increments of not more than 100 feet. (b) Check the barometric scale of sensitive altimeters to ensure they are calibrated in millibars and increments of not more than 2 millibars. (c) Replace any altimeter that fails either or both checks. Note: Millibars are equivalent to hectopascals. Compliance: Prior to 28 March 1996 unless previously accomplished in accordance with AD/BAL/15, or Prior to issue of a Certificate of Airworthiness. Background: Reports have been received of altimeters calibrated in metres being supplied for Balloon use. As all aircraft altitudes and airways clearances are provided in feet, and barometric scale settings are stated as millibars, this Directive is issued to require that altimeters installed in balloons are calibrated in appropriate units.