PA-28R Cherokee Arrow All Series
Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 150; Flight Crew Total 430; Flight Crew Type 40
Aircraft Equipment Problem Less Severe
Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft
Aircraft X was a recent purchase by the company and had recently come out of maintenance and inspection after the purchase. I was the member of the company who had the most time in the particular aircraft. In comparison to the other PA-28-201 the company owned; Aircraft X seemed under powered; regularly backfired during ground operations; and consistently had fouled plugs. I regularly told the maintenance department about my perceived discrepancies. The maintenance department performed inspections looking for any noticeable issues; none to my knowledge were found.  Approximately one week prior to the engine failure while preforming a post flight inspection my student noticed an oil slick along the left cowling. During the flight; no noticeable indications of an oil leak were noticed. The maintenance department removed the cowling and upon further inspection both left valve covers were leaking oil. Upon further inspection three bolts were missing from each valve cover; and all remaining bolts were loose. One mechanic remarked that he had never seen anything like this happen before. He also quoted how he remembered checking the torque of all the valve cover bolts during the previously completed annual.The following is an account of what happened during the flight where the engine failure occurred. The purpose of the flight was training/review in preparation for the student's check ride. The student was a Private Pilot with an Instrument Rating and approximately 250 hours total time.Conducted engine run up near departure end. Noticed left Magneto running rough. Leaned mixture to burn off fouling; after leaning procedure both magnetos passed required check. Departed straight out; then turned right for south departure. Set climb power; noticed fuel flow was low; about 10-11 gallons per hour with mixture control set to full rich. Engine ran rough for less than 0.5 sec; then regained normal power. CFI turned on fuel pump as precaution.Entered power off stall at 6000 ft MSL. During power reduction; no engine roughness noticed. Recovered from power off stall; during recovery using full power intermittent engine roughness noticed by student. Vibration felt through yoke; CFI did not feel vibration. CFI decided to return; with student flying. As student reduced power to descend; engine roughness increased. Fuel flow reduced to approximately 6 gallons per hour with mixture control full rich. Student returned power to full and engine roughness decreased but remained continuously. When power increased to full; fuel flow increased to 9 gallons per hour. CFI took control of the aircraft.5 miles south of ZZZ approximately 5000 ft MSL CFI called Tower and [advised of] engine roughness; requested landing. Turned to make long straight in due to low descent rate resulting from required high power setting to prevent engine roughness. Approximately 6 mile right base; CFI asked student to run engine troubleshoot checklist. Both magnetos operated satisfactory; alternate air made engine roughness increase in severity; engine oil pressure; engine oil temperature; and fuel pressure all in the green. Approximately 3 mile straight in CFI made right 360 to descend more and get on glide path. Approximately 2 mile final about 2300 ft MSL CFI lowered gear to reduce airspeed to below flap speed. 1 mile final set flaps 10 degrees; on short final set flaps 25 degrees. During power reduction to flare engine roughness increased substantially. Touched down at about 80 KIAS; with throttle at idle; engine barely running and shuttering during roll out. CFI increased throttle to full to clear runway; engine seemed unresponsive. CFI pulled mixture to idle and engine stopped. Coasted to stop near hold short line on and taxiway. Student completed securing aircraft checklist. CFI assessed outside conditions for fuel leak or fire; none were present. CFI called tower and said that emergency services were no longer needed; and requested a tow vehicle. Student and CFI pushed aircraft clear of runway hold short line and waited for airport personnel.The maintenance department performed an inspection on Aircraft X. The two bolts holding the flange of the intake tube on the left rear cylinder had fallen out. One of the bolts was recovered from the bottom of the cowling; the other was not recovered. The intake tube had disconnected form the cylinder head and had fallen and laid on the exhaust tube below it. Upon further inspection; the rubber gasket connecting the intake tube to the intake manifold had cracked.
PA28R Flight Instructor reported engine roughness that resulted in the engine being unresponsive after landing.