IFR Fix: 'Only localizer minimums authorized'

The pilot leveled the single-engine Cessna in cruise, leaned the mixture, and surveyed the scattered clouds below. They appeared to be thickening; time to divert. Now there’s a new problem: no response coming to the pilot’s efforts to contact the alternate airport’s control tower.

Well, it’s a holiday; maybe the tower closed early. The pilot continued inbound, making position reports and watching for light gun signals (in case the aircraft radios had failed). No beam of light appeared, so the pilot landed—remembering during shutdown that one of the steps taken while leaning the mixture by ear had been to lower the radio volume. It had never been turned back up.

Some weather, a self-inflicted communications glitch, and the distraction of diverting had forged the error chain; the idea of an early holiday tower closing then explained away the radio silence and the absence of light signals.

It’s always a good idea to verify the tower’s operating hours if, by delay or design, you expect to make an after-hours landing.

Arriving IFR? Check whether the tower’s closing changes procedures or limits your options.

Typically, Class D airspace reverts to Class E when a control tower closes for the day. Class C airspace also may revert, as this note in the Airport/Facilities Directory for the Portland, Maine, International Jetport describes: "AIRSPACE: CLASS C svc ctc APP CON svc 1045–0500Z‡ other times CLASS E."

Approach minimums could be affected by the tower schedule if weather reporting stops at closing time. Many approach plates contain notes instructing pilots to raise minimums or visibility when using an alternate altimeter setting. 

Pilots flying the ILS or LOC RWY 16 approach to Hawkins Field in Jackson, Mississippi, must sift through numerous variations in procedure. Depending on their aircraft’s approach category, they also must comply with specialized minimums for using the UTUWI fix; minimums for an inoperative medium intensity approach lighting system; and minimums for an inoperative MALSR combined with using an alternate altimeter setting.

Don’t stop reading the note at that point if you fly an aircraft in slower approach categories, because its final section applies to you too—and would spare you from thinking, as the Cessna pilot did, that one of your electronic components had failed.  "Glideslope unusable when control tower closed; only localizer minimums authorized during this period," said the approach plate valid from Sept. 18 to Oct.16.