In the case of Aeroperu Flight 603, a fatal crash was caused by duct tape that was accidentally left over some or all of the static ports on the underside of the fuselage after the aircraft was cleaned. As the static ports are critical to the operation of virtually all of those flight instruments that provide aerodynamic data regarding airspeed, altitude and vertical speed to the pilots and to the aircraft's computers, this bit of duct-tape caused the total failure of multiple basic flight instruments.
Another crash was caused for a similar reason: pitot tubes that were blocked by an insect led to flight instrument failure, and later, a tragic crash. This was Birgenair Flight 301.
These accidents happened in the mid-1990s. Today, two decades on, are there better systems in place to ensure that static ports or pitot tubes don't get blocked, causing instrument failure?
Edit 1: In both these flights, the pre takeoff checks missed out on the blocked static ports/pitot tubes. Human error clearly happened at this stage. Question is, have an steps been taken to make the flight instruments proof to this particular human error?