Narrative:

I was on a cross country from march AFB, ca to las vegas mccarran, nv. While descending through 4000-3500 ft MSL a moderate to severe vibration occurred. Not knowing what had occurred I began to evaluate (after maintaining control of the aircraft) what the problem was. All engine instruments checked and all structural parts seemed to be ok. Not knowing what might occur during the next few seconds I chose to make an emergency landing on runway 25L. It seemed like the easiest runway to glide to. Unfortunately, a 757 was told to go around. I knew at the time it wasn't necessary but I hadn't the time to talk to anyone. Prevention: the problem was mechanical in nature. A cylinder rocker arm 'gasket' (holder) let loose. The vibration was caused by a cold cylinder. As a pilot I had no idea what this emergency would feel like therefore I could not have known how long the engine would have run before it ceased. Callback conversation with reporter revealed the following information: reporter stated that he was just handed off to the tower from approach control when the engine severe vibration happened and he 'went' for the runway underneath him which was runway 25L. Therefore, he never completed the switch to the tower frequency to advise them of the problem until after landing. He then taxied off to parking with the vibrating malfunctioning engine. There was no apparent investigation by the FAA. The aircraft was an T-41, or cessna 172. Believing that the B757 was going for the right runway is why he chose the left runway, but he does not remember exactly!

Google
 

Original NASA ASRS Text

Title: INSTRUCTOR OF A SMA SEL TRAINING FLT MADE FORCED LNDG AT DEST ARPT WHEN THE ENG STARTED VIBRATING.

Narrative: I WAS ON A XCOUNTRY FROM MARCH AFB, CA TO LAS VEGAS MCCARRAN, NV. WHILE DSNDING THROUGH 4000-3500 FT MSL A MODERATE TO SEVERE VIBRATION OCCURRED. NOT KNOWING WHAT HAD OCCURRED I BEGAN TO EVALUATE (AFTER MAINTAINING CTL OF THE ACFT) WHAT THE PROB WAS. ALL ENG INSTS CHKED AND ALL STRUCTURAL PARTS SEEMED TO BE OK. NOT KNOWING WHAT MIGHT OCCUR DURING THE NEXT FEW SECONDS I CHOSE TO MAKE AN EMER LNDG ON RWY 25L. IT SEEMED LIKE THE EASIEST RWY TO GLIDE TO. UNFORTUNATELY, A 757 WAS TOLD TO GAR. I KNEW AT THE TIME IT WASN'T NECESSARY BUT I HADN'T THE TIME TO TALK TO ANYONE. PREVENTION: THE PROB WAS MECHANICAL IN NATURE. A CYLINDER ROCKER ARM 'GASKET' (HOLDER) LET LOOSE. THE VIBRATION WAS CAUSED BY A COLD CYLINDER. AS A PLT I HAD NO IDEA WHAT THIS EMER WOULD FEEL LIKE THEREFORE I COULD NOT HAVE KNOWN HOW LONG THE ENG WOULD HAVE RUN BEFORE IT CEASED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE WAS JUST HANDED OFF TO THE TWR FROM APCH CTL WHEN THE ENG SEVERE VIBRATION HAPPENED AND HE 'WENT' FOR THE RWY UNDERNEATH HIM WHICH WAS RWY 25L. THEREFORE, HE NEVER COMPLETED THE SWITCH TO THE TWR FREQ TO ADVISE THEM OF THE PROB UNTIL AFTER LNDG. HE THEN TAXIED OFF TO PARKING WITH THE VIBRATING MALFUNCTIONING ENG. THERE WAS NO APPARENT INVESTIGATION BY THE FAA. THE ACFT WAS AN T-41, OR CESSNA 172. BELIEVING THAT THE B757 WAS GOING FOR THE R RWY IS WHY HE CHOSE THE L RWY, BUT HE DOES NOT REMEMBER EXACTLY!

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.