SA-227 AC Metro III
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 100; Flight Crew Total 3300; Flight Crew Type 500
ATC Issue All Types; Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft
I am a line pilot and training Captain; training a transition trainee in the SA227. The trainee was the pilot flying in the Captain's seat and I was pilot not flying seated in the copilot's seat. After an uneventful takeoff my trainee completed his climb flow and checklist and we proceeded to be vectored on to our outboard course. At what appeared to be around 3;000 FT AGL; my trainee drew my attention to his pitot-static instruments. When I first saw them; his airspeed was at zero (actually; the needle looked like it was trying to rotate around counter-clockwise from zero); his altimeter appeared to be frozen at around 2;000 FT; and his VSI was showing a 100-200 FT/minute descent. At this point in time; we were established in the climb with climb power set. Normally; the SA227 with this amount of weight on board would be at about 160-180 KTS and climbing around 700-1;000 FT/minute. After comparing his instruments to mine and judging our height about the ground; it appeared as though my instruments were indicating properly. Thinking this could be a clogged static line; I instructed my trainee to open the pilot's alternate static source. Upon doing this; the instruments did not seem to be affected at all. Puzzled by this; I instructed my trainee to cycle the pilot's alternate static source valve open and closed repeatedly a few times. After trying this with no changes; I tried to think of any other instrumentation malfunction scenarios that could make this type of indication. As I thought about it; I noticed that the VSI was now showing a slight (200-300 FT/minute) climb and that the altimeter was not indicating around 2;500 FT and increasing. Thinking the problem might resolve itself; I decided to continue climbing for a little while longer. As I made this decision; ATC then asked us to 'maintain at least 500 FT/minute in the climb for terrain'. When ATC said this; I noticed that the transponder was still on system 1 (pilot's side altitude encoding). At this point; I decided to abandon trying to resolve the problem and I took control of the airplane and returned back to [departure airport]. As we returned I explained to ATC that the pilot's instruments were malfunctioning and that the copilot's instruments appeared to functioning normally. After mentioning that the transponder was encoding altitude data from the faulty static system; I asked ATC if he wanted me to switch it to the copilot's system but he declined and instructed me to cease squawking altitude. We were in IMC for a few moments during the very last portion of the climb/troubleshooting effort but as soon as I requested to go back; I descended almost immediately back into VMC. We continued in VMC all the way back. As we descended; after passing approximately 2;000 FT; my trainee noticed that his airspeed was starting to increase; his altimeter was starting to indicate near actual altitude; and his VSI was showing a normal descent rate. Once we landed; his altimeter was indicating field elevation; his VSI was zero; and his airspeed matched my airspeed during the landing roll out (and associated airspeed callouts). Upon investigation by maintenance; they discovered that a static line had broken off of the back of one of the instruments on the pilot's side and that pressurized cabin air was entering the pilot's static system thus causing the erroneous and misleading indications.
SA227 Captain reported returning to departure airport because of abnormal pitot static indications that were later traced to a broken static line behind one of the instruments.