Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
General None Reported / Taken
Procedure
I was a passenger on...a 737.  It had been snowing; prior to our pushback and the aircraft was deiced at the gate before departure.  Type I and type IV fluids were applied.  This is the second time that I have personally witnessed an inadequate application of type IV fluid.  The wing was striped orange and green after the application.  The snow and all precipitation had ended so I did not feel that this was worthy of reporting to the crew.  I was going to try to speak to them after we landed to let them know to be on the lookout for this; but they had already left the aircraft when I deboarded.To be clear; there was no jeopardy for this particular flight as the precipitation had ended.  There was also no requirement for the crew to do a wing check as the precipitation had ended so the crew would have never known otherwise.The safety issue is that as a crew; you expect a complete application of the proper fluid.  If there had been more precipitation; there would have been a danger of the fluid not providing an adequate anti-ice protection as the type IV application was not done correctly.  It almost appears as if they are skimping on the amount of fluid to save money.
An air carrier Captain flying as a passenger on a B737 witnessed an incomplete Type IV de-icing application prior to gate departure; a failure he had previously experienced himself.  As there was no current precipitation he opted not to attempt to contact the flight crew until the end of the flight; but they had deplaned prior to his being able to do so.