The Senate is concerned about the F-35s electronic warfare ability in relation to production quality affecting apertures on the airframe, Reuters reports.
Apertures are a tough thing to design for stealth aircraft. The aircraft has to be stealthy, yet let antennas and radar detectors peak through the skin without creating adverse radar concerns.
The F-35 has 10 apertures that pertain to radar detection as can be seen from this graphic.
As a comparison, the F-22--sometimes described as an antenna farm--has around 30 apertures on the airframe.
Production quality has nagged the F-35 program even while proponents complain more aircraft need to be built per year. The problem with building a higher quantity of F-35s is that what is currently being built are "mistake-jets" because of production knowledge immaturity.
The electronic warfare concern may have been one of the classified issues mentioned in last years DOD "quick-look" report" pointing to a variety of F-35 troubles.
Electronic warfare is an interesting term with the F-35. It has no wide field of view self-defense jamming equipment. One of the assumptions is that the narrow-band and narrow field of view radar in the nose will perform some jamming functions. Due to the cooling issues and sustained power with AESA radars, this is probably not a very reliable function. The aircraft will have narrow-band, mostly nose-on low-observable capability and some expendable decoys. A towed decoy--combat proven in ALLIED FORCE 1999--is not expected until Block 4. Whenever that happens.
A paper on predicted F-35 survivability can be read here.