Cyberlimb is legal. MADs aren't image scanners, they're fairly simple. If there is metal they go *ping*.
For an illegal, metal weapon inside a metal cyberlimb, they go ... ? 
After pinging a MAD scanner, if you're subjected to a physical or visual search (ie; being patted down, or showing your cyber limb), then the non-metal materials don't matter. If they put you through a cyberware scanner, then the non-metal materials don't matter.
Ping, or a quiet beep, or an AR pop-up. Whatever. You're not going to have sirens going off every time someone with a Data Jack, or forgets to take off a belt and walks through a check point. TSA doesn't scramble a SWAT team each time something pings at an airport, it's an incredibly dull, routine activity. Handled quietly (most of the time), and they are literally running down an internal check list. "Did you completely empty your pockets?" "Are you wearing a belt?" blah, blah, blah.
And yes, possibly your cyberlimb will be subject to a pat down. *shrug* If they're able to spot a -10 concealment with a perception test, you were likely screwed anyway. But you should have a considerable dice pool advantage on this check.