B737-700 Flight Crew experiences Captain's pitot static instrument failure at rotation. The aircraft had been on the ground for 36 hours in a snow and ice storm before this departure. Maintenance found ice in the plumbing of both pitot static systems.
Synopsis
B737-700 Flight Crew experiences Captain's pitot static instrument failure at rotation. The aircraft had been on the ground for 36 hours in a snow and ice storm before this departure. Maintenance found ice in the plumbing of both pitot static systems.
Narrative
When we arrived the aircraft was covered in a thick covering of snow and ice. The aircraft had not flown the day before and accumulated a large amount of contaminates on the aircraft surfaces. There was no contaminates in the engines and the fan section turned freely. After engine start we were directed to taxi to the deice pad. Two vehicles arrived and began to deice the aircraft which were joined by another two vehicles after twenty minutes. This process took about two hours to complete before the Deice Coordinator declared the aircraft free of contaminates. After the engines were started; we taxied the aircraft for departure when we received a radio call from the Deice Coordinator that he spotted some contaminates still on the aircraft. We returned to the deice pad; configured the aircraft for deicing; and had the deice truck remove any contaminates they found. This deice process took another twenty minutes. We were cleared for takeoff and after V1; when the First Officer made the rotate call; I noticed we were about five knots slow. This got my attention as I waited about one second and starting rotating the aircraft. The aircraft nose was off the ground and I got multiple warnings on the PFD for airspeed and altitude disagreement along with a momentary stick shaker. I noticed the airspeed was rolling back to 45 knots and the altitude was remaining on field elevation. A buffet alert was displayed on the CDU as well. A quick glance and the First Officer's PFD showed normal indications and; after we retracted the gear; I gave him the aircraft. We got an immediate call from ATC wanting to know our altitude which I gave off the First Officer's altimeter. I quickly selected the number two position on the transponder to avoid further ATC interruptions. We climbed to 6000 feet and informed ATC that we needed to return but needed radar vectors to troubleshoot the problem and prepare for an approach. I ran the QRH checklist while the First Officer flew the aircraft; but we did not recover the Captain's airspeed or altitude indications. We elected to burn down fuel to landing limits. We received a clearance for a visual approach and on short final in visual conditions; a one-second windshear warning was received with no external indications or indications on the First Officer's instruments. Considering the circumstances and the very real possibility the system was getting inaccurate information from the Captain's altimeter and airspeed; the First Officer stated his intention to continue to land. I concurred and a normal flaps 30 landing was flown by the First Officer . After returning to the gate; Contract Maintenance found ice contaminates in both the left and right pitot static systems.In severe ground icing conditions; a cover should be placed over the static ports to prevent introduction of contaminants into the -700 pitot static system. Ground Deicing Crews should be trained repeatedly about the dangers of getting deice fluid in pitot static ports during deice and anti-ice operations.
Second reporter narrative
We were originating the aircraft which had sat on the ramp during a major snowstorm for approximately the past thirty-six hours. The aircraft was completely coated in snow/ice to the point that I could not read the writing on the winglets during the preflight inspection. The engines were noted to be free of ice and snow. It was a normal engine start and taxi to a remote deice pad. The Ice Man advised that his two trucks probably did not have enough fluid to deice our aircraft so a Contract Deicer took over. Even with as many as four trucks spraying our aircraft; it took almost two hours to clean the aircraft with no precipitation falling. We received the clean aircraft clearance from the Contract Deicer and began the taxi to the runway. During the taxi; we received a call from Operations saying our personnel had observed additional contaminates on the tail of the aircraft so we returned to deice pad for further removal by Company employees. That complete; we taxied to the runway. I was the Pilot Monitoring. At rotation; the Captain remarked that he was receiving unreliable airspeed and altimeter information; and; after observing that my instruments appeared accurate; transferred control of the aircraft to me and selected the number two transponder to assist ATC. Approach Control should be commended for their handling of the situation as they accommodated our requests without hesitation and offered to arrange ground assistance should we need it. We were able to complete an uneventful flaps 30 visual approach. After returning to the gate; Contract Maintenance reported that they had discovered frozen internal plumbing on both static ports; which they subsequently thawed; drained; and dried. After completing the requisite paperwork; we again departed; this time uneventfully.I am not an engineer so I do not know how to fix the frozen plumbing issue on the static ports. But I do know that I would not prefer to find out about it at rotation. We were fortunate in that it was VFR and that my instruments worked correctly. Suppose it had been low IFR and my instruments had also failed; then we would have had a full-blown emergency.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.