estimated that more than half of the approaches made in their line operation were nonprecision.
On January 12, 1971, Southern Airways issued changes to their DC-9 Operating Manual as follows:
(1) A note was added to the Nonprecision Approach and Landing Diagram stating that, for a short approach where time expiation and MDA for the approach are expected to coincide, flaps may be extended to 50° at the approach fix.
(2) An additional callout at 500 feet above minimum altitude was added.
(3) The discussion of use of the radio altimeter was modified to include a warning that the system was unreliable over hilly or rolling terrain, and should not be used for altitude information.
Southern Airways' authority for charter operations was contained in its Operation Specifications. This authority required that any "off-route" operation by accomplished as prescribed by Part 121 of the Federal Aviation Regulations applicable to supplemental air carriers and commercial operators, and by the exceptions which were contained in their Operations Specifications. The exception applicable to IFR takeoff and landing weather minima required that, when the pilot-in-command was not qualified for the airport, he must use the weather minima and instrument approach procedures prescribed in Part 97 of the Federal Aviation Regulations. The minima established for a localizer approach, by this part of the regulations, were 350 feet and 1 mile. However, the minima specifically established for supplemental air carriers or charter operations at the Tri-State Airport were 412 and 1 mile.
The airport and route qualifications applicable to the charter flight in this instance were stated in Part 121.445 as follows:
"(a) Each supplemental air carrier and commercial operator shall establish in its manual a procedure whereby each pilot who has not flown over a route and into an airport within the preceding 60 days will certify on a form provided by the operator that he has studied and knows the subjects listed in paragraph (b) of this section in regard to the routes and airports into which he is to operate.
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