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Squawk the squawkSquawk the squawk

Imagine this situation: A client scheduled for a single-engine commercial checkride arrives for one final practice session, only to find engine oil on the cockpit floor.

Tracing it back shows that the line driving the complex single’s mechanical oil pressure gauge has begun to leak. His highly experienced CFI decides to fly the airplane anyway, putting the candidate through the full roster of commercial maneuvers on a day that 30-knot gusts and the accompanying turbulence could hardly be expected to make loose connections any more secure. Only after the flight do they report the problem to the airplane’s operator, who promptly grounds it. (The checkride, scheduled for the following day, is postponed.)

Hard to believe? It happened to a good friend who is not prone to exaggeration. Another friend (flying with a different operator) had the heading indicator fall out of the panel into her lap during the initial climb of the long solo cross-country for her private certificate. She decided the compass provided guidance enough, and completed the flight.

There are a couple of differences in kind between these two events. The second operator was notorious for cutting corners (and is no longer in operation). The first is known for strict procedures and a rigorous maintenance philosophy, making it appear that its instructor was acting on his own initiative. But both point to a single question: When would you prefer that CFIs (or solo students) squawk an aircraft rather than fly it with something not quite right?

Even criteria that initially appear clear-cut aren’t always. We hope there’s broad agreement that any deficiency that makes an aircraft unairworthy grounds it immediately and until remedied. However, even airworthiness can be somewhat subjective. Recall that its definition has two components: conformance with the type certificate, which is less ambiguous, and being in condition for safe operation, where reasonable opinions may differ. (No doubt the first CFI’s argument that a spurt, or even seep, of oil into the cockpit isn’t a safety hazard would prove highly imaginative.)

And context makes a difference. You might not let a failed vacuum pump scrub a daylight VFR flight around the pattern or in the practice area, but would you want that airplane dispatched on a cross-country? And how late in the afternoon would you be comfortable sending it out in order to be certain it is back on the ramp before dark?

Discrepancies in nonessential equipment require balancing short-term revenue loss against the risk of doing additional—and increasingly expensive—damage if repairs are deferred. Much depends on how definitively you can identify the nature of the failure. If the number two radio will receive but not transmit, the problem is likely to be inside the radio itself; swapping it with number one could help confirm that. But if number two’s circuit breaker keeps popping, the possibility of a wiring fault can’t be discounted. Nor can it be assumed that the problem is limited to that circuit. Recall that the catastrophic 2007 fire that destroyed NASCAR’s Cessna 310 was precipitated by a short in the circuit powering the weather radar—equipment that wasn’t even needed for that flight. And if the problem really is the radio, you still might be more comfortable flying it from the nontowered Dubois, Wyoming, airport than inside the Washington, D.C., Special Flight Rules Area, where the consequences of lost communications make reliance on a single transceiver less appealing.

A reasonable rule for students is to get a second opinion when there’s even a trace of doubt. Of course, this assumes the student can recognize anomalies that aren’t specified in the preflight inspection checklist. After getting pushed sideways by a gust while landing, a renter in Arizona parked to give the Cessna 172 a once-over, decided everything looked fine, and went out to do more airwork. Back at base, the operator found that “both propeller blade tips were damaged, the fuselage skin was wrinkled, and the firewall had sustained substantial damage as a result of a hard landing.” The prop, at least, he should have noticed.

Instructors are more likely to rely on their own judgment, so firmer guidance may be in order. Even if the last tube came out clear, how much water do they have to drain from the fuel before you’d rather flush the system than risk an engine stoppage? (A couple of undetected teaspoons in the carburetor were enough to bring down a Beech Musketeer on Long Island in 2010.) Are you comfortable sending it out with more than a couple of drops of oil under any part of the engine except the breather? And is there such a thing as an acceptable amount of wrinkling in a skin or control surface? AOPA recently grounded one of its own Cessna 172s after an alert instructor noticed unexpected flexure in the elevator skin. Fixing it took two weeks—but no one had to contend with a loss of elevator authority in the meantime.

ASI Staff

David Jack Kenny

Manager, Safety Analysis
David Jack Kenny analyzes GA accident data to target ASI’s safety education programs while also supporting AOPA’s ongoing initiatives and assisting other departments in responding to breaking developments. David maintains ASI’s accident database and regularly writes articles for ePilot, Flight School Business, Flight Training, CFI-to-CFI, and other publications.

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