Date: 202007
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Tower ZZZ
Aircraft component: Cockpit Window
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Training / Qualification; Situational Awareness; Distraction
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Overcame Equipment Problem
Contributing factors: Procedure; Human Factors; Aircraft; Company Policy
Primary problem: Procedure

Narrative: During taxi out the First Officer's R2 window suddenly popped open. The First Officer closed it immediately with no further problem. During the Before Start Flow and Before Start checklist; which were conducted per the Operations Manual; the First Officer 'verified' his window closed and locked by visually observing that the window handle was full forward and apparently in the locked position. He also manually 'bumped' the handle in the 'closed/locked' direction with his fist. A move that I sometimes see from First Officers. Yet; the window popped open later; during taxi; anyway. This is the second time I've seen a window pop open in recent weeks; and in both cases; it was with a relatively inexperienced First Officer. Also in both cases; the event happened after a 'window wash' was conducted at the gate by cabin service personnel from inside the cockpit; and in both cases the cabin service person had failed to properly lock the window closed; yet leaving the handle in what appeared to be a closed-and-locked position.In both cases described above; the First Officer did his window check after the window cleaning had taken place; so 'timing' is not the issue. Basically; the window cleaning can be a 'set-up' for a problem; but our current checklist procedure; even when followed to the letter; is not effectively 'trapping' this error. In my opinion; this needs to be addressed formally. The Operations Manual contains the relevant expanded flow and checklist item; respectively. On neither page is there any note or caution that a visual observation and a manual 'fist-bump' against the handle may not be sufficient to ensure a properly locked window. My personal procedure for verifying my L-2 window is closed and locked is to fully open the window thus making sure it can be opened for a ground egress if needed!. Then; close it to locked position in one vigorous movement. The momentum of this window movement ensures that it is properly locked. I've learned from experience that anything less than this effort is a potential set-up for an insecure window and an error that is not likely to be trapped. No text on those manual pages directs a manual; physical verification of a secure window in the manner I just described. I do usually brief new First Officer's on my 'technique' and encourage them to use the same technique; but it is strictly a technique and obviously insufficient to ensure fleet-wide safety regarding this item. This Operations Manual omission could contribute to a window popping open during takeoff; which could lead to more serious problems. We were fortunate in both cases that it happened during taxi-out rather than takeoff. It seems likely that crews have experienced this same issue during taxi but may not have reported it; so the number of such occurrences is not really known and thus this problem isn't getting attention.I highly recommend that a 'note' or 'caution' be added to the Operations Manual that the window handle can appear to be closed and locked; and even 'feel' closed and locked with a fist-bump; when it isn't; and that a more deliberate manual operation of the mechanism is necessary to ensure proper window security. In addition; perhaps a 'blast message' to the B737 fleet is in order. Better to make these minor changes now than after the NTSB recommends them in an accident report.Cabin service personnel leave cockpit windows apparently closed and locked but not really secure. A lack of guidance in the Operations Manual to mitigate against this potential threat. A 'note' or 'caution' should be added to the Operations Manual that the window handle can appear to be closed and locked; and even 'feel' closed and locked with a fist-bump; when it isn't; and that a more deliberate and complete manual operation of the mechanism is necessary to ensure proper window security. In addition; perhaps a 'blast message' to the B737 fleet is in order.




Synopsis: B737 Captain reported the First Officer's window came open while taxiing. The Captain reports this is a recurring issue in the aircraft type with First Officer's not be trained correctly to ensure their window is secured.