Narrative:

I was cruising at 5000 ft. The air was smooth and the attitude of the airplane never moved from level. Occasionally the altimeter would jump about 100 ft abruptly, then come back to 5000 ft. The airspeed indicator and vsi would also jump. ZHU reported that my encoder was showing 4700 ft. I replied that I was level 5000 ft. I knew I had a static system problem, but this airplane wasn't equipped with an alternate static source. It was VFR out and since this was a rental airplane, I didn't want to break the vsi. The altimeter started going crazy and went all the way down to 4400 ft, then back up to 4800 ft, where it stabilized. When I got on the ground at jan, I discovered the source of the static problem. It had been a very long day. Before the flight, I helped the aircraft owner (a&P and CFI) change the oil in the aircraft. I helped put the cowl on and then went inside while he ran up the aircraft. I had preflted the aircraft earlier and it was otherwise ready to go. My passenger and I jumped in the aircraft after the owner gave us the thumbs up. I didn't double- check to verify that the oil cap was put back on, and it wasn't. Oil had streaked out of the cowling and down the side of the aircraft, right over the static port. I cleaned up the mess, added oil and flew home. The encoder was 100-200 ft low when I asked jan approach to give me the altitude showing on the way back to new. When the altimeter started jumping around, I did report it to ZHU. Relearned an old lesson. Never trust anyone, always check. The saying about people who assume rings true.

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Original NASA ASRS Text

Title: PLT OF AN SMA SEL ACFT EXPERIENCED ERRATIC INDICATIONS OF THE ACFT XPONDER ALTIMETER, ALTIMETER, AIRSPD AND VERT SPD INDICATORS DURING LEVEL FLT CRUISE.

Narrative: I WAS CRUISING AT 5000 FT. THE AIR WAS SMOOTH AND THE ATTITUDE OF THE AIRPLANE NEVER MOVED FROM LEVEL. OCCASIONALLY THE ALTIMETER WOULD JUMP ABOUT 100 FT ABRUPTLY, THEN COME BACK TO 5000 FT. THE AIRSPD INDICATOR AND VSI WOULD ALSO JUMP. ZHU RPTED THAT MY ENCODER WAS SHOWING 4700 FT. I REPLIED THAT I WAS LEVEL 5000 FT. I KNEW I HAD A STATIC SYS PROB, BUT THIS AIRPLANE WASN'T EQUIPPED WITH AN ALTERNATE STATIC SOURCE. IT WAS VFR OUT AND SINCE THIS WAS A RENTAL AIRPLANE, I DIDN'T WANT TO BREAK THE VSI. THE ALTIMETER STARTED GOING CRAZY AND WENT ALL THE WAY DOWN TO 4400 FT, THEN BACK UP TO 4800 FT, WHERE IT STABILIZED. WHEN I GOT ON THE GND AT JAN, I DISCOVERED THE SOURCE OF THE STATIC PROB. IT HAD BEEN A VERY LONG DAY. BEFORE THE FLT, I HELPED THE ACFT OWNER (A&P AND CFI) CHANGE THE OIL IN THE ACFT. I HELPED PUT THE COWL ON AND THEN WENT INSIDE WHILE HE RAN UP THE ACFT. I HAD PREFLTED THE ACFT EARLIER AND IT WAS OTHERWISE READY TO GO. MY PAX AND I JUMPED IN THE ACFT AFTER THE OWNER GAVE US THE THUMBS UP. I DIDN'T DOUBLE- CHK TO VERIFY THAT THE OIL CAP WAS PUT BACK ON, AND IT WASN'T. OIL HAD STREAKED OUT OF THE COWLING AND DOWN THE SIDE OF THE ACFT, RIGHT OVER THE STATIC PORT. I CLEANED UP THE MESS, ADDED OIL AND FLEW HOME. THE ENCODER WAS 100-200 FT LOW WHEN I ASKED JAN APCH TO GIVE ME THE ALT SHOWING ON THE WAY BACK TO NEW. WHEN THE ALTIMETER STARTED JUMPING AROUND, I DID RPT IT TO ZHU. RELEARNED AN OLD LESSON. NEVER TRUST ANYONE, ALWAYS CHK. THE SAYING ABOUT PEOPLE WHO ASSUME RINGS TRUE.

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.