United Airlines, the world's second-largest airline carrier by revenue-passenger-miles behind American Airlines, was forced to ground its entire Boeing 777 fleet and cancel flights to carry out re-examinations on the jets’ suppression system.

UA’s cancellation of flights continues a series of similar measures taken by other airline carriers amid mounting airline maintenance and inspection practices and questions about Federal Aviation Administration oversight.

United Airlines, the world’s third-largest carrier by total operating revenues, has canceled 37 of its 84 daily flights with 777s, jets mostly used for flights to Europe and Asia. The company is currently working to complete the inspections of the suppression systems by tomorrow, spokeswoman Megan McCarthy said.

The cancellations and grounding weren’t requested by the FAA, the administration said in a statement.

“Everyone is erring on the side of caution, partly to send a message that the system works and partly just to be cautious. It seems like the system is responding in an appropriate manner,'' said Richard Aboulafia, director of aviation for consulting firm Teal Group in Fairfax, Virginia according to Bloomberg.com.

Four other American airline carriers have taken similar measures of groundings and flight cancellations to carry out inspections that haven’t been made good enough or in some cases weren’t made at all.

United Airlines said in a statement that it found out during a standard review of maintenance records that tests on a fire suppression system in the cargo hold had not been meticulous enough. UA willingly told the FAA about the problem.

"United will not operate these aircraft until the tests are complete," said UA, the world’s fourth-largest carried by total passengers transported, in the statement.

UA said that more cancellations are possible on Thursday. The company deployed other aircrafts and rebooked passengers on different airlines.

Southwest Airlines started the series of cancellations. The carrier grounded dozens of 737s to carry out missed structural inspections. After inspectors found fuselage cracks on some aircrafts, the FAA proposed to fine the carrier with $10.2 million (5.1 million pounds).

US Airways Group was next in line and the company grounded six 757s for inspections.
American Airlines also canceled on March 26 nearly 10 percent of its air traffic, the equivalent of approximately 200 flights, to check on wiring bundles in its MD-80 planes.

Then Delta Air Lines then followed. The carrier also canceled flights to carry out inspections at wiring bundles on certain planes. Nearly 430 MD-80s were inspected by both carriers.