TACAN Lock-on Error - 1965



On return to Adak from a routine patrol the third-pilot/navigator of the P3 was in the left seat. (Note: these were the days when crews had only one NFO who was TACCO. The new/junior 3P normally worked the Nav Table and DRT) The weather was well above minimums, 1000 overcast, with 7 miles visibility, so I decided to pass up the usual GCA and let the young third pilot shoot a TACAN approach. After a few turns in the holding pattern at the initial approach fix we commenced approach, in the clouds with GCA monitoring us. Everything looked good on the 12-mile arc except that I didn’t think the third pilot had pulled enough power off to make it down to 1500 ft at the seven-mile gate hut I decided not to say anything and see how he would handle it.

        After awhile I switched my Horizontal Situation Indicator (HSI) bearing indicator selector to ADF to cross-check our position; it showed us well past our inbound bearing, but since our birddog had been unreliable the last few flights I figured that it was no good and switched back to TACAN.

        We were just passing 3500 ft when we approached the inbound bearing (or what we thought was the proper one) and I remarked that we were going to be high at the seven-mile arc and suggested we take off some power to make 1500 ft at seven miles. About this time we got in some heavy turbulence which made me wonder about things (there was a strong south wind). As I was reaching to switch the bearing selector to ADF again, GCA called, saying that they had a faint target east of the field and requested our altitude.

        A fast switch to GCA control, switch to ADF on the HSI, a level off, then we climbed to 3500 ft. Reevaluation of the situation revealed we were indeed east of the field flying in the clouds over 2400-ft peaks.

        The flight was terminated with a normal GCA with a 40-degree error in the TACAN all the way into 3 miles. All I can say is thank goodness for GCA and 3Ps that are inadvertently high on TACAN approaches. If we had been at 1500 ft approaching what we thought was the seven mile gate the flight surely would have been terminated by the mountains east of the field.

Note: The author of this story is unkown. If he will identify himself, I'll give him credit. WebMaster

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