Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
General Release Refused / Aircraft Not Accepted
Weather; Human Factors
Due to unrelated complex MEL/ground equipment issues; the flight left the gate solely for the purpose of heating the cabin using engine bleeds (APU and ground heat unavailable) and to complete aircraft deicing due to frost from overnight.  This was completed.  After deicing and warming the aircraft; the flight returned to the gate to board PAX and depart.  While at the gate; ice was still observed adhering to the fuselage in proximity to the main cabin door by both PAX and ground crew.  In addition; a deadheading (DH) pilot also observed ice.  Further examination showed that while the wings were clean and clear of contaminants; ice was still in fact found on the upper forward fuselage; and in the vicinity of the vertical stab.  The contaminant was not just frost; but appeared to be ice accumulated during an approach previously.  The aircraft was deiced again and the Ice Crew was instructed to do a more thorough post deice inspection. The Ice Crew did a good job of removing the frost.  However; the combination of extreme cold (below zero F) and night conditions for de-icing made it difficult for them to see and remove the extra contaminant.  The obvious threat is failure to comply w/ clean aircraft concept.  Had this flight been proceeding out for T/O (as is almost always the case) it would have left with contamination.  I do not consider this to have been a very high threat IN THIS CASE as the wings were clear and the horizontal stab appeared to be so as well; however; it is obvious that in a different scenario with other contaminants missed during the post deice inspection report an incident or accident could occur.  The station crew and de-ice crew did not seem to rush the job or seem negligent in any way; I believe the conditions and scenario created a situation where extra vigilance was required and they did not catch the ice.In the northern cities we sometimes find ice accumulation from the previous evening's approach when the conditions include extreme cold.  It is generally considered not a big deal; as we frequently deice for this or; as in this case; frost.  In the future; if deicing for frost; we will verbally verify the crew is aware of the extra contaminant and the inspection verifies the removal of such.
After de-icing of the gate; a CRJ700 Captain reports returning to the gate to board passengers. During boarding significant ice is noticed still adhering to the fuselage and a second de-icing is accomplished prior to takeoff.