What is the GPS performance in extended or autonomous navigation mode?

[johnl]

If a GPS satellite cannot get navigation data from the Control Segment, it can either transmit stored ephemeris (extended navigation) or calculate its position using other satellites (autonomous navigation). Is there any information on real life performance? Is this something common?

 

[johnl]

Think I've got the answer. Extended navigation is something quite frequent, so it can't be very bad. Autonav is not used at all and will probably be removed from GPS ICD.