Are jet aircraft still at risk of hijacking by people wielding melee weapons? Are jet aircraft still at risk of hijacking by people wielding melee weapons (as opposed to explosives)?

I thought that aircraft were designed post-9/11 such that passengers can't enter the cockpit, but Wikipedia's list of hijackings mentions incidents this decade which involved melee weapons:


  China June 29, 2012: an attempt was made to hijack Tianjin Airlines
  Flight GS7554 from Hotan to Ürümqi. Six people tried to hijack the
  aircraft 10 minutes after take-off. There were 6 police officers on
  board. Four were in plain clothes, taking the plane for a business
  trip. The hijackers used aluminium canes with sharpened tips to attack
  the members of the crew. The police officers and civilians on board
  subdued the hijackers, all of whom were of Uyghur ethnicity. The plot
  was foiled and the plane returned to Hotan in 22 minutes after
  takeoff.
United Airlines Flight 93 history shows that melee weapons are not very efficient: the passengers that are likely to outnumber hijackers at least ten to one can win if they are willing to fight. 

The question remains, how likely is that passengers will go into risks to show the resistance. If it is just about changing the course to land in the different airport, they may choose to be quiet. If they have nothing to lose, I think the hijackers have no chances.