Investing.com -- Boeing (NYSE:BA) shares were lower in premarket U.S. trading on Tuesday after two airlines reportedly discovered loose parts on some grounded models of the planemaker's 737 Max 9 jet, threatening to compound growing safety concerns following a dangerous mid-air blowout on an Alaska Airlines flight last week.
According to a statement from United Airlines (NASDAQ:UAL) quoted by industry publication The Air Current, preliminary inspections into its 737 Max 9s found that the aircraft had "instances that appear to relate to installation issues in the door plug." These problems included bolts on several panels that "needed additional tightening."
Alaska Airlines (NYSE:ALK) also said late on Monday that initial reports from its technicians found some "loose hardware" on some of its 737 Max 9s. The carrier added that it is continuing to wait for final documentation from Boeing and the U.S. Federal Aviation Administration before beginning the formal inspection process.
Concerns over the Max 9 -- a version of Boeing's single-aisle plane that has about 10 more seats than the popular Max 8 -- have been heightened since a panel on an Alaska Airlines-operated flight blew out en route from Portland, Oregon to Ontario, California last Friday. The pilots were able to turn the jet around and land it safely.
"The safety of these aircraft is our priority and we will take the time and steps necessary to ensure their airworthiness, in close partnership with the FAA," Alaska Airlines said in a statement on its website.
Outside of the U.S., an airline in India found a missing washer on a Boeing 737 Max aircraft, according to media reports citing a statement from the country's Directorate General of Civil Aviation. Boeing recommended that a one-time inspection of all 737 Max jets in India be conducted for loose hardware, the reports added.
Meanwhile, Michael O'Leary, Chief Executive of Boeing-customer Ryanair (LON:0RYA) (NASDAQ:RYAAY), told the Financial Times in an interview that the company and its rival Airbus "need to significantly improve quality control." Ryanair operates variants of the 737 Max that is different than the one involved in the Alaska Airlines incident.