Section 139.315 - Aircraft rescue and firefighting: Index determination(a) An index is required by paragraph (c) of this section for each certificate holder. The Index is determined by a combination of-(1) The length of air carrier aircraft and(2) Average daily departures of air carrier aircraft.(b) For the purpose of Index determination, air carrier aircraft lengths are grouped as follows:(1) Index A includes aircraft less than 90 feet in length.(2) Index B includes aircraft at least 90 feet but less than 126 feet in length.(3) Index C includes aircraft at least 126 feet but less than 159 feet in length.(4) Index D includes aircraft at least 159 feet but less than 200 feet in length.(5) Index E includes aircraft at least 200 feet in length.(c) Except as provided in § 139.319(c) , if there are five or more average daily departures of air carrier aircraft in a single Index group serving that airport, the longest aircraft with an average of five or more daily departures determines the Index required for the airport. When there are fewer than five average daily departures of the longest air carrier aircraft serving the airport, the Index required for the airport will be the next lower Index group than the Index group prescribed for the longest aircraft.(d) The minimum designated index shall be Index A.(e) A holder of a Class III Airport Operating Certificate may comply with this section by providing a level of safety comparable to Index A that is approved by the Administrator. Such alternate compliance must be described in the ACM and must include: (1) Pre-arranged firefighting and emergency medical response procedures, including agreements with responding services.(2) Means for alerting firefighting and emergency medical response personnel.(3) Type of rescue and firefighting equipment to be provided.(4) Training of responding firefighting and emergency medical personnel on airport familiarization and communications.Doc. No. FAA-2000-7479, 69 FR 6424 , Feb. 10, 2004; Amdt. 139-26, 69 FR 31522 , June 4, 2004