B757-200
Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Workload; Physiological - Other
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Diverted; General Maintenance Action; General Declared Emergency
Aircraft
At FL400 shortly after leveloff; we noted a haze in the cockpit which soon developed into light smoke emanating from behind the instrument panel. We quickly donned our oxygen masks; declared an emergency; and began an immediate descent into a divert airport. We performed the QRH 'Smoke; Fire; and Fumes' and after step 10; 'EQPT Cooling Switch - ALTN' and step 15; 'Rt Pack - Off;' we noticed that the light smoke abated leaving a residual haze in the cockpit.  We flew an ILS approach to Runway XX; landed; cleared the runway; had fire and rescue check the aircraft for any signs of fire; and then taxied to the ramp.Maintenance was troubleshooting the aircraft after landing and was concentrating on an equipment cooling fan and an equipment cooling filter.
Shorty after leveling at our cruise altitude of FL400; I began to smell a very faint odor. I looked toward the back of the cockpit (behind the Captain's seat) and saw a 'light haze' which was illuminated by the cockpit lighting (the 'light override' switch on the overhead panel was on which turned on the cockpit dome light). I advised the Captain of this and for the next few minutes we investigated the issue to see if we could determine the source of the 'haze'. All aircraft systems appeared normal and no circuit breakers were popped. After a few minutes; the 'haze' appeared to be getting thicker and I could see what appeared to be light white smoke in front of both sides of the instrument panel. At this point we donned our oxygen masks and established crew communications. The Captain declared an emergency with Center and requested a descent and clearance to a divert airport which was approximately 80 NM on the nose. During the descent we completed the Smoke; Fire or Fumes Checklist. At Step 16 of the checklist; we were instructed to wait 2 minutes to see if the smoke was going to continue. At this point; the smoke appeared to start decreasing and the 'haze' in the cockpit seemed to be clearing. As a result; the checklist was complete. We continued toward the divert airport and were vectored to the ILS for Runway XX. I continued to fly the aircraft until we were established on final and then the Captain assumed control of the aircraft for a normal landing. After landing; we turned off of the runway and stopped the aircraft to assess the situation. The cockpit was clear of smoke and everything looked normal so we taxied to the Ramp. Emergency vehicles followed us to parking as a precaution and we also remained on oxygen until block-in.The cause of the event is unknown at this time but it did seem to be resolved by accomplishing the Smoke; Fire or Fumes Checklist. Of note; as a result of accomplishing the checklist; both Utility Busses were turned off (Step 5); the Recirculation Fan was turned off (Step 6); and the Right Pack was turned off (Step 15). The Left Pack remained on for the entire flight.
A B757 crew declared an emergency; and diverted to a nearby airport after completing the Smoke; Fire or Fumes Checklist for an odor and white smoke in the cockpit.