Narrative:

During walk-around; observed excessive amount of oil or grease on belly of right side of aircraft. Area extended from aft of wheel well; to rear of aircraft; into outflow valve; to tail-skid. Made logbook entry and called maintenance. Maintenance advised that substance was sealant and aircraft would be scheduled for wash at a later time. Logbook stated that aircraft had already received wash four days prior. [We] contacted maintenance control who verified that aircraft had received a wash four days prior. Due to large amount of substance and color and also the fact that aircraft had recently been washed; refused to accept aircraft for safety of flight concerns until source of substance could be positively identified. [There was a] logbook entry 17 days prior for acm [air cycle machine] replacement; [another] logbook entry 13 days prior for odor in cabin. Advised maintenance control; dispatch and local maintenance.

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Original NASA ASRS Text

Title: B737 Captain discovers an excessive amount of grease and oil on the belly of the aircraft during preflight; running all the way to the tail. When maintenance cannot positively identify the source of the lubricant the aircraft is refused.

Narrative: During walk-around; observed excessive amount of oil or grease on belly of right side of aircraft. Area extended from aft of wheel well; to rear of aircraft; into outflow valve; to tail-skid. Made logbook entry and called Maintenance. Maintenance advised that substance was sealant and aircraft would be scheduled for wash at a later time. Logbook stated that aircraft had already received wash four days prior. [We] contacted Maintenance Control who verified that aircraft had received a wash four days prior. Due to large amount of substance and color and also the fact that aircraft had recently been washed; refused to accept aircraft for safety of flight concerns until source of substance could be positively identified. [There was a] logbook entry 17 days prior for ACM [Air Cycle Machine] replacement; [another] logbook entry 13 days prior for odor in cabin. Advised Maintenance Control; Dispatch and Local Maintenance.

Data retrieved from NASA's ASRS site as of April 2012 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.