Tempest Aero Group has issued Service Bulletin SB-012 (FAA Notice Number NOTC5147) because of reports of cracking on the hex nut of select lot numbers of Tempest spark plugs. The bulletin applies to spark plugs manufactured between May 5, 2026 and July 29, 2026, and it calls for the immediate inspection of the affected spark plugs prior to the aircraft’s next flight, and of course the replacement of any plugs with cracks.
Dealing with the bulletin is pretty straightforward. Determine if a spark plug is included in the affected lots (see the table) using a visual inspection of the stamping on the plug. If an affected spark plug(s) is found, remove it from the engine and visually inspect for cracks as shown in the Figure 1 and 2 below. Be sure to inspect any affected spark plugs that are in inventory.
If cracks are found, replace the spark plug(s). If replacing with new Tempest spark plug(s), verify the new spark plugs carry compliance stamp SB012 as shown in Figure 4 below. If no cracks are found, reinstall spark plug(s), return the aircraft to service via the appropriate maintenance manuals, and make a maintenance log entry noting compliance with the Service Bulletin.
Tempest wants all cracked plugs returned, and it agreed to pay for “reasonable” labor costs to remove and replace spark plugs affected by the Service Bulletin, plus it will reimburse shipping costs to return the plugs. Tempest said the estimated time to accomplish this Service Bulletin is 1.5 hours for four-cylinder engines and 2 hours for six-cylinder engines including removal, inspection, and reinstallation. Tempest can send replacement plugs in advance, but customers must return the cracked ones within 30 days or they’ll be invoiced. As an example, the typical price of a single Tempest UREM40E plug is $41.
Tempest lists Wyette Lowe, Director of Technical Support, as a contact for help at 336-551-2183 and email SB012@tempestaero.com
Inspection — easy. Replacement — tricky. The Aircraft Spruce guys told me yesterday that the plugs for my IO-550 (Tempest URHB32E) or not available anywhere at the moment, nor are their Champion equivalents.
Kudos to Tempest for being out front with this problem. That action is in stark contrast to Champion products.
Champion changed their manufacturing process in an effort to lessen production costs a few years ago.. Many unairworthy spark plugs that exceeded allowable specifications of resistance were shipped. Very soon the problem manifested itself as the spark plugs began to misfire in flight. The word got out, and mechanics installing these plugs began checking their resistance before installing them. Many were found that were out of tolerance right out of the packaging. To my knowledge, Champion never acknowledged the problem. No service bulletins or Airworthiness Directives were issued. I understand that Champion subsequently changed the manufacturing process again, but did not recall any of the batch of plugs that contained defective plugs that had already been distributed.