Two mechanics report finding unapproved access holes in the lower belly section of the external fuselage skin of various Eurocopter BK-117 helicopters. The holes were used to access the fuel transfer tube attach clamps that tend to leak fuel when flying from warm weather to frigid winter weather states.
Synopsis
Two mechanics report finding unapproved access holes in the lower belly section of the external fuselage skin of various Eurocopter BK-117 helicopters. The holes were used to access the fuel transfer tube attach clamps that tend to leak fuel when flying from warm weather to frigid winter weather states.
Narrative
This aircraft; [Eurocopter BK-117]; has a hole in the belly between the fuel pumps. The hole was there when we got the aircraft from the Repair Station in ZZZ. There is tribal knowledge that many; if not all; BK-117s have these holes. The aircraft has most likely been operating with this hole for years and years. There is a clamp on the fuel transfer tube that can seep. The hole is for access to the clamp; as opposed to removal of the cabin floor; which would otherwise be needed for access. I was informed by Mechanic X that there was an issue with these holes. He told me that Eurocopter had issued a 'No Technical Objection' (NTO); requiring a daily tap test and repair in 50 hours. A daily tap test requirement indicated to Mechanic X and me that this is a serious issue; so we took pictures of ours and sent to our Manager for evaluation right away. We took the aircraft out of service until we received guidance from Eurocopter.I do not recall ever seeing a BK-117 that did not have these holes. Our BK had this hole when it came from the Repair Station in ZZZ. Countless people; including [those] with far more experience than me had accepted this hole; so I did not believe that it was an improper repair until I heard from Mechanic X. Nevertheless; I had signed-off the aircraft with this condition.I would suggest a Service Bulletin (SB) from Eurocopter or possibly a Maintenance bulletin from our Company Operations. When I talked to the [Manufacturer] Technical Representative about our aircraft he said that there were many other aircraft having the same issue. The hole was known since October 2009. It was only identified as an issue April 2011.
Second reporter narrative
[I was] informed by another Mechanic that his aircraft had a hole in the belly that had been filled with a [body filler]. When we did our airworthiness check we looked and found a similar hole. It has been known that most [BK-117s] have holes like this. Did not believe it to be an issue until it was passed down from another Mechanic who had a similar hole. We then took action to fix the issue. Informed Eurocopter and they sent a 'No Technical Objection' (NTO) for the inspection of the hole while a repair is being worked on. Suggest [we] have a complete drawing of the aircraft belly with all the holes in it.
NASA callback
Reporter stated there are two different holes in the lower fuselage belly skin that are discussed. One of the holes is a manufactured fuel drain hole about one-eighth of an inch (1/8 inches) in diameter that enlarges over time and eventually requires a sheet metal repair to reduce the opening. The other belly hole is an access hole that has appeared on many of their BK-117 helicopters; but is not a Eurocopter approved hole. The belly section of the BK-117 is only .012 inches thick metal skin with an inner bonded honeycomb layer; basically a composite skin; which can delaminate.Reporter stated the daily tap test is used to locate delamination around the unapproved holes until a permanent repair can be accomplished within 50 hours. His company filed an FAA Form 337 for a major repair of the fuselage. When or how the unapproved access holes started appearing on the lower belly skin; no one seems to know. Some of the access holes looked like someone had taken a hatchet to the fuselage skin.Reporter stated that although the holes are 'not approved' by the Manufacturer; they do provide easy access to the fuel tank transfer tube attaching clamps. The clamps apparently leak fuel; especially in the winter when outside temperature changes drastically when flying from warm weather in the southern states into frigid winter temperatures in the northern states. Since the access holes are 'not approved;' they all must be repaired. When the clamps leak fuel; mechanics will have to remove the cabin floor to gain access to tighten the transfer tube clamps. Reporter stated; the Manufacturer does not seem interested in issuing a Service Bulletin allowing the fuselage belly skin to be modified for access to the clamps.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.