Why does the F-35 Lightning II have only 1 crew when the F/A-18 Hornet had 2?
According to program officials involved in the development of the F-35, the F-35 is a single seat aircraft because:
New advances in avionics and sensor fusion technology, which can
allow a single pilot to perform missions that previously required two
Given the fact that the F-35 is build around the concept of
Network Centric Warfare there is less cockpit workload for most strike missions. Consequently, the need for a co-pilot is a lot less.
The single-seat configuration also maximizes commonality between the
three variants of the F-35 thereby keeping development costs low.
The survivability of the F-35 includes limiting the probability of detection. Ergo, a two-seater version can very easily increase the RCS of the F-35 thereby compromising its stealth capabilities
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That said, one major drawback that remains on the one seat design is the demand on one pilot to assimilate and decide on all the information available.