Fuel issues prompt United 787 Mayday.

A “fuel Mayday” from a United Airlines Boeing 787 landing in Sydney from Los Angeles sparked what may be the world's shortest road closure as part of an emergency response on Thursday. The captain of an aircraft is required to declare a fuel Mayday if fuel falls below the reserve level an aircraft is required to have when it reaches its destination, often about 45 minutes. The procedure is designed to alert air traffic controllers to the fuel shortage and allow them to give the plane landing priority. READ UNITED to debut 787-10 on enhanced transcon routes. It does not mean an aircraft is running out of fuel and, in this case, it is understood the 787  still had 39 minutes of fuel remaining. The Mayday shortly after 6am meant fire and medical crews were placed on standby while  New South Wales police closed roads in the busy airport precinct as part of "a full emergency response". They were re-opened just three minutes later. “The NSWPF traffic control plan was activated at 6.36am, with some major roads surrounding the airport being closed as a precaution,'' police said. “The plane landed safely without incident and the roads re-opened at 6.39am.” An Airservices Australia spokeswoman said the pilots were following procedures and the aircraft had not been in any danger. The aircraft taxied to the gate  and passengers disembarked normally. United said the flight landed at Sydney International Airport "following a mechanical issue". A United Boeing 777  bound for San Francisco had to return to Honolulu in 2016 because  of  fuel "overburn" caused by strong headwinds. Flight 724 was forced to turn around two hours into its flight because the aircraft did not have enough fuel to make it to San Francisco.