Date: 202002
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Aircraft: B767-200
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Climb
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Window Ice/Rain System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Time Pressure
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; Flight Crew Landed in Emergency Condition; General Maintenance Action; General Evacuated
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During climbout at about 10 minutes after departure while climbing through about 15;000 feet the Captain noticed the same non-normal odor on the flight deck experienced two days prior. We called the mechanic who was on our jumpseat up to try and locate the source of the odor. After about a minute of not being able to locate the source of the odor; we sat the mechanic down and donned oxygen. It was apparent that the issue had not been fixed and a source of the odor could not be readily determined; we advised ATC. We are given a heading and a descent to return to ZZZ. As I was the pilot flying; the Captain started working through 'Smoke; Fire or Fumes' QRH and once completed; the descent and approach checklists. As we are in an expeditious descent as pilot flying; I had kept the speed at above 250 KIAS under 10;000 feet as a part of our authority to get the plane on the ground in the soonest amount of time. We set up for the ILS into ZZZ and were given vectors to the final approach course and tracked the ILS in for a normal landing. After touchdown; a right turnoff the runway was made and after the parking brake was set; the 'Evacuation Checklist' was completed. We vacate the aircraft via a set of mobile air stairs and wait as the fire crew clear the aircraft. During the postflight; the mechanic onboard deemed that the source of the odor was near the Captain's overhead panel and possible from the wiring harness associated with the window heat system.


Second narrative: Between approximately 5-10 minutes after takeoff; during climb; and while climbing through 15;000 feet; the First Officer and I noticed an acrid smell in the cockpit. The First Officer and I; called the supernumerary mechanic forward to help identify the source of the fumes. The three of us; identified the location as primarily on the left side of the cockpit. The three of us talked about it briefly as we climbed; but could not clearly identify the location and affected system. The smell became more noxious to me as the fumes increased in intensity; I commanded the crew to go on oxygen. The First Officer continued to fly the aircraft and I opened the QRH to the 'Smoke; Fire or Fumes' checklist. We advised ATC; leveled off at FL200 and asked for an expedited descent and return to ZZZ.Center immediately gave us a vector direct to ZZZ and a descent. With changes to the FMC for the diversion and approach; we were able to get to step 24 in the QRH checklist as we approached 4;000 ft. I elected at that point to concentrate on safely navigating and flying the aircraft to the approach and landing at ZZZ and did not have time to proceed further in the QRH. I did have time as we descended; to sample the air to see if the fumes were continuing; increasing; or decreasing in accordance with the checklist. At each point in the checklist; I very briefly pull my mask slightly away from my face and sampled a short breath of air from the cockpit to see the condition of the fumes as indicated in the QRH. The fumes were still present; but decreasing very slightly at each check. At no time did the crew notice visual indications of smoke.To expedite our descent and maintain an expedited profile to ZZZ; we did go above 250 KIAS below 10;000 feet. At approximately 7;000 feet we were below 250 KIAS.We were given priority handling with vectors to Runway XX at ZZZ. The approach was flown and landed normally. The aircraft safely exited the runway at the first available taxiway. The aircraft was stopped immediately after clearing the runway. The crew ran the Evacuation checklist; where crash fire rescue personnel and equipment met the aircraft. The crew noted no fume smell as we exited the cockpit. We opened the L1 door; and because we did not smell fumes at that position; to avoid injury; we elected to use the air stair that the fire department had immediately available outside the aircraft.In the past; I have had electrical fires on aircraft that have the smell of ozone. That was not the smell. It was also not a petroleum type smell. I can only characterize it as an acrid chemical smell that I have only ever encountered on this aircraft; the day before under the same conditions. I cannot say for sure weather it is a smell associated with a chemical fire or simply chemical fumes.On post flight; after the fire department declared the aircraft safe; the supernumerary mechanic began a more thorough inspection from a sitting position in the left pilot seat. He was able to locate the area directly above the left forward window as the source of the smell; by putting his face directly against the panel covers overhead the window. On further inspection with the aircraft powered in the ramp parking; with panels removed; the mechanic believes he found the source to be the wiring harness for the windows; however these findings are very preliminary and should not be relied on until further maintenance action; and investigation.


Synopsis: B767 flight crew reported experiencing a burning smell in the flight deck resulting in a return to the departure airport.