Class D Transit Without a Transponder
You are pilot-in-command of a two-seat ultralight, empty mass 280 kg and maximum takeoff mass 450 kg, cruising at 75 kt. You plan a 38 nm flight from a private strip to a farm strip. The direct route crosses a Class D control zone from the surface to 2,500 ft MSL. Your State’s rules require two-way radio and a serviceable Mode A/C transponder for Class D entry. Your aircraft has a working VHF radio but no transponder. Weather is VFR: visibility 15 km, cloud base 4,000 ft AGL, wind 210/10, QNH 1018. Fuel is 20 L usable, burn 16 L/h, and the legal VFR reserve is 30 minutes. You call ATC; the controller replies: “Remain outside Class D; expect clearance in 20 minutes.” Your destination is 15 nm beyond the zone boundary. The only nearby alternative is a 22 nm diversion to an uncontrolled strip with no fuel. You have 1 h 15 min total endurance. Decide.
1. Does the ATC reply allow you to enter Class D, and what equipment rule governs the decision?
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No. “Expect clearance” is not a clearance, and ATC cannot waive the equipment requirement. Your State’s Class D rule requires both a two-way radio and a serviceable Mode A/C transponder. You have the radio but not the transponder, so you may not enter the zone even if ATC later says “cleared into Class D.” The correct action is to remain outside the lateral boundary, establish a safe holding orbit clear of the zone, and not let the aircraft drift inbound while you talk or navigate. If you need to change route, do it outside controlled airspace. The controller’s estimate is not authorization.
2. Evaluate the fuel and diversion options. What is the safest legal course of action?
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Total endurance is 75 min. With a 30-min reserve, 45 min is available before reserve. Waiting 20 min then flying 15 nm at 75 kt (12 min) uses 32 min, leaving 13 min above reserve; waiting 20 min then diverting 22 nm (18 min) uses 38 min, leaving only 7 min. But the transponder rule means the expected clearance cannot be issued to this aircraft, so waiting has no legal benefit. Divert immediately: 22 nm at 75 kt takes about 18 min, landing with roughly 57 min of fuel, well above reserve. The no-fuel alternate is a planning problem, not a reason to enter Class D illegally. Land, refuel, and proceed only by an approved route or after fitting a transponder.
3. If your radio fails while you are outside the zone, what should you do?
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If the radio fails outside the zone, remain clear of Class D and follow lost-communication procedures. Without a transponder you cannot squawk 7600, so use light signals if available and avoid the zone. Navigate to the diversion strip, land, and telephone ATC. Do not enter Class D to “sort it out”; a radio failure does not create an exemption. If you are already committed to a route that requires the zone, turn away early and use the alternate. Record the time and maintain terrain clearance.