A thorp T18 in cruise at 6500 ft declared an emergency and diverted due to complete loss of oil quan...

Attributes
ACN	420435
Time
Date	199811
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zzz
State Reference	US
Altitude	msl bound lower : 6500 msl bound upper : 6500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : zzz
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other landing other
Route In Use	enroute : on vectors
Flight Plan	None
Person 1
Affiliation	company : air carrier
Function	flight crew : single pilot
Qualification	other other : other pilot : commercial pilot : cfi pilot : instrument
Experience	flight time last 90 days : 24 flight time total : 3388 flight time type : 1975
ASRS Report	420435
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

I had just completed an annual inspection on my experimental thorp T18 in my role as an a&P mechanic. As part of that annual, I complied with airworthiness directive 98-02-08 which required removal of the crankshaft plug to inspect the bore for corrosion. None was found and a new plug was installed. On the subsequent test flight, after 45 mins in the air, the plug blew out releasing copious amount of oil, which totally obscured the windshield (4 qts lost in 5 mins). A request for priority handling at ZZZ airport led to a successful landing. A second plug was installed by the local FBO. That plug also failed on the return flight, although not with the total obscuration of the first failure. I question the wisdom of airworthiness directive 98-02-08. 2 plug failures, the first with near disastrous consequences, in 1 day suggests to me that field installation of those pugs may invite more difficulty than the rare defects that procedures would allegedly uncover. I found no defects nor have any been found by other mechanics I have discussed this with. Callback conversation with reporter revealed the following information: the reporter stated this incident occurred after the reporter performed the annual inspection and complied with airworthiness directive 98-02-08 on the lycoming engine. The reporter said the airworthiness directive consists of removing the crankshaft plug at the forward end, checking for internal corrosion then replacing the plug. The reporter stated the plug is a press fit plus similar to a freeze plug on an automobile engine block. The reporter said after the emergency landing at ZZZ an FBO mechanic again replaced the plug, which leaked on the return flight but did not result in complete loss of oil. The reporter said this airworthiness directive invites more trouble than it seeks to uncover. The reporter said the directive came about due to a crash when a crankshaft failed and internal corrosion was discovered but the aircraft also had a propeller strike and several other factors which contributed to the crankshaft failure.

Original NASA ASRS Text

Title: A THORP T18 IN CRUISE AT 6500 FT DECLARED AN EMER AND DIVERTED DUE TO COMPLETE LOSS OF OIL QUANTITY AND PRESSURE AND WITH VISION IMPAIRED BY AN OIL COVERED WINDSHIELD. INCIDENT CAUSED BY CRANKSHAFT PLUG FAILURE.

Narrative: I HAD JUST COMPLETED AN ANNUAL INSPECTION ON MY EXPERIMENTAL THORP T18 IN MY ROLE AS AN A&P MECH. AS PART OF THAT ANNUAL, I COMPLIED WITH AIRWORTHINESS DIRECTIVE 98-02-08 WHICH REQUIRED REMOVAL OF THE CRANKSHAFT PLUG TO INSPECT THE BORE FOR CORROSION. NONE WAS FOUND AND A NEW PLUG WAS INSTALLED. ON THE SUBSEQUENT TEST FLT, AFTER 45 MINS IN THE AIR, THE PLUG BLEW OUT RELEASING COPIOUS AMOUNT OF OIL, WHICH TOTALLY OBSCURED THE WINDSHIELD (4 QTS LOST IN 5 MINS). A REQUEST FOR PRIORITY HANDLING AT ZZZ ARPT LED TO A SUCCESSFUL LNDG. A SECOND PLUG WAS INSTALLED BY THE LCL FBO. THAT PLUG ALSO FAILED ON THE RETURN FLT, ALTHOUGH NOT WITH THE TOTAL OBSCURATION OF THE FIRST FAILURE. I QUESTION THE WISDOM OF AIRWORTHINESS DIRECTIVE 98-02-08. 2 PLUG FAILURES, THE FIRST WITH NEAR DISASTROUS CONSEQUENCES, IN 1 DAY SUGGESTS TO ME THAT FIELD INSTALLATION OF THOSE PUGS MAY INVITE MORE DIFFICULTY THAN THE RARE DEFECTS THAT PROCS WOULD ALLEGEDLY UNCOVER. I FOUND NO DEFECTS NOR HAVE ANY BEEN FOUND BY OTHER MECHS I HAVE DISCUSSED THIS WITH. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THIS INCIDENT OCCURRED AFTER THE RPTR PERFORMED THE ANNUAL INSPECTION AND COMPLIED WITH AIRWORTHINESS DIRECTIVE 98-02-08 ON THE LYCOMING ENG. THE RPTR SAID THE AIRWORTHINESS DIRECTIVE CONSISTS OF REMOVING THE CRANKSHAFT PLUG AT THE FORWARD END, CHKING FOR INTERNAL CORROSION THEN REPLACING THE PLUG. THE RPTR STATED THE PLUG IS A PRESS FIT PLUS SIMILAR TO A FREEZE PLUG ON AN AUTOMOBILE ENG BLOCK. THE RPTR SAID AFTER THE EMER LNDG AT ZZZ AN FBO MECH AGAIN REPLACED THE PLUG, WHICH LEAKED ON THE RETURN FLT BUT DID NOT RESULT IN COMPLETE LOSS OF OIL. THE RPTR SAID THIS AIRWORTHINESS DIRECTIVE INVITES MORE TROUBLE THAN IT SEEKS TO UNCOVER. THE RPTR SAID THE DIRECTIVE CAME ABOUT DUE TO A CRASH WHEN A CRANKSHAFT FAILED AND INTERNAL CORROSION WAS DISCOVERED BUT THE ACFT ALSO HAD A PROP STRIKE AND SEVERAL OTHER FACTORS WHICH CONTRIBUTED TO THE CRANKSHAFT FAILURE.

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.

A thorp T18 in cruise at 6500 ft declared an emergency and diverted due to complete loss of oil quantity and pressure and with vision impaired by an oil covered windshield. Incident caused by crankshaft plug failure.