April 17 (Reuters) - Boeing's manufacturing practices, at the center of a full blown safety crisis following a Jan mid-air panel blowout, will come under scrutiny on Wednesday in two U.S. Senate hearings.

Boeing has been grappling with a crisis that has undermined its reputation following the Jan. 5 mid-air panel blowout on a 737 MAX single-aisle plane. It has undergone a management shakeup, U.S. regulators have put curbs on its production, and deliveries fell by half in March.

The U.S. Senate Commerce Committee is holding a hearing with members of an expert panel that released a report in February criticizing the planemaker's safety culture and calling for significant improvements.

A later session is expected to feature testimony and documents from Boeing whistleblower Sam Salehpour, a current engineer at the company, his lawyers said.

Salehpour has claimed that Boeing failed to adequately shim, or use a thin piece of material to fill tiny gaps in a manufactured product, an omission that could cause premature fatigue failure over time in some areas of the Boeing 787 Dreamliner.

Boeing has challenged Salehpour's claims against two of its widebody jets, the 787 and 777, which fly internationally. Boeing said on Monday it has not found fatigue cracks on in-service 787 jets that have gone through heavy maintenance. (Reporting By Allison Lampert in Montreal, Editing by Nick Zieminski)