The San Francisco Airport had intentionally disabled a navigation system in the weeks before the crash on 6 July of Asiana Airlines Flight 214.
The crash that killed at least two of 307 people on board occurred at the end of a visual approach by the Boeing 777-200ER flight crew to Runway 28 Left.
That runway normally operates an instrumented landing system navigation aid to help in bad weather or fog. The system helps pilots detect the approach path and manage the glide slope until the crew is in visual contact with the runway. But the system is out of service for three months while there is construction on the other end of the runway. The airport is increasing the size of the runway safety zone on Runway 28L to comply with new federal standards.
By increasing the size of the runway safety zone, the construction project is intended to help pilots avoid the type of short landings that may have occurred with Flight 214.
A San Francisco airport official was asked in a press conference on 6 July about the possible relevance of the deactivated ILS aid to the crash, but he dismissed it by citing the approach that was carried out under visual flight rules.
If the flight crew had access to the ILS beacon, however, they would have received automated updates alerting them if their glide slope was too steep.
Airport officials said they have found no evidence establishing a cause of the crash so far, but US Federal Bureau of Investigation said there was no indication of a terrorist attack.
The US National Transportation Safety Board has dispatched a go-team assembled from Washington DC and the Pacific Coast. Asiana Airlines also has vowed to fully cooperate with the investigation, and has established an emergency response centre at their corporate headquarters.