Aircraft maker Boeing has denied fresh allegations about production faults affecting the quality of its aeroplanes.
On Tuesday, the company rejected criticism from a former employee that some 787 Dreamliner aircraft could have a shortened service life because the company had taken technical "shortcuts" to speed up production.
A Boeing spokesman emphasized that the allegations were incorrect and had already been investigated by the US Federal Aviation Administration (FAA).
"These claims about the structural integrity of the 787 are inaccurate and do not represent the comprehensive work Boeing has done to ensure the quality and long-term safety of the aircraft," Boeing said in a statement.
The company is facing new public questions about its quality oversight after the allegations came to light. A subcommittee of the US Senate is planning a hearing in the middle of next week with the former Boeing employee as a witness.
Quality oversight at Boeing has been at the centre of attention since an incident in January. Shortly after take-off, a piece of the fuselage of a virtually new Boeing 737-9 Max belonging to the US carrier Alaska Airlines broke off. None of the more than 170 people on board were injured.
According to initial investigations, the NTSB accident investigation authority assumes that four fastening bolts were missing from the fuselage section.
It is known that the fuselage fragment, a door-plug, was removed at the Boeing factory for maintenance and then reinserted. However, the company has not yet been able to find any documentation on this and make it available to the investigators.
In March, Dave Calhoun announced he will leave his role as chief executive of Boeing at the end of the year.