Date: 201201
Location: ZZZ.Airport, US
Light: Night
Aircraft: EMB ERJ 190/195 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight phase: Parked
Second aircraft: EMB ERJ 170/175 ER/LR
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Anomaly: Other Unsafe work environment
Detector: Person Maintenance
When detected: Other Maintenance
Result: General None Reported / Taken
Contributing factors: Equipment / Tooling; Company Policy
Primary problem: Company Policy

Narrative: I am submitting this report to report an unsafe working environment at the ZZZ Maintenance hangar. The hangar floor; particularly under the Heavy C-check area; is hollow and appears to be unstable. As I have learned since working here over the years; when this hangar was originally built in the 1940's the offices; bathrooms; hallways and such were all underground. This situation apparently worked fine for them; but they were building much smaller aircraft; in a factory setting. As of now; it appears that the basement has been backfilled and access to the basement obviously sealed off. In 2010; when a Mechanic was using a floor jack to jack up an EMB-170 Left-Hand (L/H) Main Landing Gear (MLG); once the gear was lifted up the floor jack went right through the floor. I was present at that time and reached in the hole to get the jack that was lying on gravel about a foot underneath the floor. Inside the hole I could see a large open void which appeared to be a bathroom underneath the floor.Management was informed of the incident and shown the hole in the floor and hired a company to fix it. While the repaired section of the floor appears solid; the surrounding floor still appears to be hollow and unsafe. Currently we have an EMB-190 aircraft sitting over that section of concrete floor; up on jacks; with the Main Landing Gear removed. Every time a Mechanic working in the wheel wells or under the wings drops a tool on the floor; it makes a very unsettling; hollow noise. If this section of floor would give out and the plane slips off the jacks; there is no question that many mechanics or inspectors would be killed or hurt. This is an old hangar; not originally designed to handle the weight of these aircraft; manlifts; toolboxes and stands that we have sitting on them. I believe we should no longer ignore this issue and ask for any assistance that you can provide to have this floor examined by true professionals or engineers.I'm not exactly sure why this issue has gone on as long as it has; other than assuming someone else has brought up; or that the floor was properly fixed the first time; or scared to say anything to Management.

Callback: Reporter stated his Air Carrier hired an outside Engineering company  to determine the  structural  condition of the Hangar's concrete floor.  The Engineering company drilled eleven; four inch diameter  holes in the floor for core samples.  He was told the cause of the hollow sound under the floor was due to air pockets between the newer  two inch  thick floor he was working on that  had been poured over the older  forty inch concrete.Reporter stated  the Engineering  company  informed him the concrete floor appeared strong enough to handle the  increase weight of the EMB 190 aircraft.  However; when asked about why the flooring collapsed; when the  weight of only an EMB-170 left Main Landing Gear on  a jack; sent the jack through forty-two inches of concrete; no response was given by the Engineering company.Reporter stated they are still waiting for the official results from the Engineering company. Currently; no improvements have been made; everyone expects the floor to collapse again under the increase weight of the EMB-190 aircraft.



Synopsis: A Mechanic reports about an unsafe working environment at their company Maintenance Base hangar where the floor under the Heavy C-Check line for their EMB-170/190 aircraft is hollow and appears unstable; raising concerns about serious injuries. An aircraft jack had previously collapsed through the floor when jacking an EMB-170 aircraft.