Maintenance Safety Tip-1405

Is the Duct Ready for Flight?

On November 16, 2013, a Piper PA-28-140 lost engine power shortly after takeoff and crashed, resulting in a destroyed aircraft and a seriously injured pilot. Why? Read on.
 
You are probably very familiar with the air ducts commonly referred to as “SCAT,” “SCEET,” “CAT,” and “CEET.” You may have replaced some on the aircraft engines you have worked. You might even keep a ready supply on hand. Although we are not going to go into detail about each duct here, we do caution you to ensure that the one you are using is acceptable for the particular application intended. Beware! Although it “looks like a duct,” “feels like a duct,” or “fits like a duct,” it may not function like the “approved” duct for your specific job. 
 
Investigation revealed that the “SCAT” duct installed as a carburetor air inlet duct on the mishap PA-28-140 did not meet the specifications of the air duct authorized and provided by Piper. The duct COLLAPSED, thereby cutting off air flow to the engine.
 
An approved Piper inlet duct is engineered and designed to operate in a vacuum of -12 inches of HG (mercury), at temperatures between -65 to +500 degrees Fahrenheit. The wire supporting the duct is .048 inches in diameter. Although the collapsed duct had the correct inside diameter, the wall thickness was thinner and the wire size was several thousandths less than the Piper duct.
 
We believe that “off the shelf” ducts may be being used as a normal replacement part instead of the authorized Piper carburetor air inlet duct. We say this because there have been no approved carburetor air inlets ducts ordered from Piper since 1999 even though the FAA registry indicates there are over 5000 registered PA-28-140 aircraft.
 
What can you do to help prevent another accident? Well, if applicable, check your fleet of PA-28-140 aircraft. Pass the word to the owners and operators who fly these aircraft, as well as your AMT colleagues that maintain these aircraft. The number one thing you can do is always research the manufacturer’s manuals to validate you are using approved replacement parts.  Finally, never replace components based on what was previously installed. Trust, but verify.
 
See Maintenance Safety Tip-1209, “Who do YOU Trust?” published August 2012. http://www.faasafety.gov/SPANS/noticeView.aspx?nid=4046.