Preflight inspections are one of our last opportunities to learn that something is wrong with our aircraft, and to fix it. Some pilots don’t avail themselves of the opportunity, however, which often leads to an in-flight event of some sort, at a minimum, or to something more dramatic. Of course, the quality of preflight inspections varies wildly with the circumstances. What might those circumstances be?
One of them is that we’re much more likely to skip something on the second or subsequent flight of the day than the first one. An airplane you landed 15 minutes earlier really doesn’t need an external inspection or a demonstration that the controls are free and correct, right? Well, maybe. Stuff can happen while airborne that you may not observe until back on the ground. And it’s always a good idea to check engine oil levels before any flight, if for no other reason than it’s a quick and easy thing to do, and the consequences of engine failure can be extreme.
At the same time, any recent modifications or newly installed equipment should be treated as suspect until proven otherwise. How you go about demonstrating to your and others’ satisfaction that the work was performed correctly depends on its nature, but we’d want to rack up a few flight hours before declaring all the bits and pieces to be airworthy. Until then, new things should get scrutinized before each flight.
It can be difficult to know what to look for during a preflight inspection. Properly assessing the implications of what you may find is another challenge. But missing a massive engine oil leak, which leaves behind evidence on the ramp and on the dipstick, takes preflight inspection omissions to a whole new level. Here’s an example of just that.
Background
On June 6, 2022, at about 1610 Central time, a Piper PA-28RT-201 Arrow IV was substantially damaged when it was involved in an accident near Northwest Florida Beaches International Airport (KECP), in Panama City, Fla. The pilot and one passenger were fatally injured; another passenger sustained serious injuries.
At about 0941, the airplane arrived and parked. Around 1100, the FBO moved the airplane to another location. The pilot returned to the airplane at about 1530, opening the baggage compartment, entering and exiting the cockpit multiple times and walking around the airplane’s nose until the two passengers arrived at about 1541. During these 11 minutes, he did not appear to spend any appreciable time inspecting the airplane’s engine or the ground below it. At about 1551, the airplane exited the FBO ramp and taxied to Runway 34.
According to ADS-B data, the airplane began its takeoff roll at about 1606 and reached a peak altitude of about 1200 feet msl. The pilot declared an emergency at about 1609. The ADS-B data show the airplane descended, made a 180-degree left turn and then continued to descend until impacting trees and terrain about 1.7 miles from the runway threshold.
Investigation
The airplane came to rest upright in an area of dense brush. All major components were located near the main wreckage. Multiple tree branches located along the debris path exhibited black paint transfer and were cut at 45-degree angles. The three-blade propeller remained attached to the engine. Its spinner was impact-damaged, all blades remained attached to the hub and one blade exhibited chordwise scratching. Flight control cable continuity was established from the cockpit to the flight control surfaces. Oil was noted along the bottom right side of the fuselage.
Examination of the engine revealed a crankcase breach near the #4 cylinder. The #4 connecting rod journal exhibited thermal damage, and bearing material was found welded/smeared to the crankshaft journal. The cylinder’s connecting rod cap, connecting rod bolts, and bearing pieces were found in the oil sump along with other metallic debris and a trace amount of oil. The oil drain plug remained seated and safety-wired to the oil sump.
Data retained in the onboard avionics showed that oil pressure at the accident flight’s engine startup stabilized at about 67 psi. Oil pressure gradually decreased as its temperature increased while the airplane taxied to the runway. Immediately before takeoff, oil pressure was down to about 10 psi. When the engine was advanced to takeoff power, oil pressure dropped to four psi.
The airplane sported newly installed “glass” instrumentation. The day before the accident flight, the pilot made an entry in the airplane’s logbook indicating he had performed the required post-installation flight test. Tachometer time at the end of that flight was 511.5 hours. The new panel was installed at 508.6 tach hours. The NTSB did not report the tachometer reading at the accident site.
According to the new instrumentation’s installation manual, the oil pressure sensor was to be mounted securely to the airplane’s structure using flexible hose and was specifically not to be installed to the engine. It stated, “Mounting the sensor directly to the engine may cause sensor failure/leakage and possibly fire.”
Post-accident examination of the airplane’s parking area revealed a trail of oil drops that led to a small puddle of oil where the airplane was initially parked. A second, larger area of oil staining, measuring about six by six feet, was found at the airplane’s second parking location, which was where the pilot conducted his walkaround and loaded passengers before starting the engine for departure. A trail of oil drops marked the airplane’s taxi route to the runway.
Probable Cause
The NTSB determined the probable cause(s) of this accident to include: “Maintenance personnel’s failure to follow the avionics installation guidance for the oil pressure sensor, which resulted in the high-cycle fatigue failure of an [oil] line, oil starvation, and the subsequent loss of engine power. Contributing to the accident was the pilot’s failure to perform an adequate preflight inspection of the airplane.”
According to the board, “Examination of the rigid oil pressure line revealed that it fractured due to high-cycle fatigue. This was likely from excessive vibration due to insufficient support of the oil pressure sensor and rigid line. The oil pressure sensor, which was part of the avionics system, was installed about 3 flight hours before the accident. The installation manual for the avionics system stated that a flexible line should be used to install the oil pressure sensor in order to minimize vibration effects. Instead, a rigid line was installed, which would have been more susceptible to the effects of vibration, including high-cycle fatigue failure.”
Oil staining was observed on the ramp at both locations where the airplane had been parked, indicating the oil line likely had fractured during the previous flight. In a classic understatement, the NTSB wrote, “Had the pilot noted and investigated the source of the oil leakage during the preflight inspection, he might have taken appropriate corrective action and avoided the accident.”
It’s hard for me to understand how the pilot could have missed the oil leak. Perhaps he was distracted. Perhaps he didn’t know better.
[su_box title=”What’s Behind Your Panel?” box_color=”#e5eaef” title_color=”#273957″ radius=”6″]
If you’re flying a simpler aircraft or one with all-electronic instrumentation, there might be only a few wire bundles behind your instrument panel. More complex and, especially, older aircraft tend to have not only the requisite wiring but can also sport a mix of flammable liquids only a few inches above your legs, thanks to mechanical gauges for oil and fuel pressure. Take care to ensure that related oil and fuel lines aren’t used to secure other components, which I’ve seen.[/su_box]
