SA-227 AC Metro III
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Aircraft Equipment Problem Less Severe
Air Traffic Control Issued New Clearance; Flight Crew Overcame Equipment Problem; Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft; Human Factors
We departed and were assigned an initial altitude/heading of 2;500 feet; 210 degrees respectively. The takeoff portion was normal.As we neared 1;800 feet; ATC advised of traffic at our 12 o'clock; 4 miles at 2;200 feet. The FO reported that we were looking. In an effort to clear the traffic; I increased pitch from 10 degrees to approximately 13 degrees for a better rate of momentary climb.As I did this; my airspeed rapidly decreased to around 70-80 knots; to which I shoved the nose over to avoid a stall and added more power. The airspeed did not build up quickly; but the Stall and Spin (SAS) indicator pointed to 'cruise;' meaning the stall vane outside was showing normal airspeed. The airspeed built up and stabilized at around 160 KTS. As I was doing this; the First Officer called 'altitude;' to which I checked my altimeter and it read 2;500 feet. Again he stated 'we are at 3;500 feet Captain.' I looked over to his instruments and his altimeter indeed showed 3;500 feet. I told the FO to get an altitude readout from ATC.At the same time; ATC cleared us to 5;000 feet. The FO responded accordingly; but did not ask for an altitude readout. I remained level at 2;500 feet and keyed the mic; asking for an altitude read out (as I don't believe the FO knew what I had requested; and I felt that CRM had already been compromised with the language barrier). ATC responded with '2;500 feet.' I said to the FO at this point 'okay; let's watch your altimeter in the climb and see what happens;' he responded with 'ok.'As I began a slow; steady climb to 5;000 feet; my airspeed indicator again rapidly decreased to about 90-100 KTS; my pitch was about 4-5 degrees nose up; vertical speed read normal; power settings were torque matched such that the hotter engine was temped at 620 EGT per SOP; and the SAS indicator again showed 'cruise.' I immediately said to the FO 'we have a pitot static issue; I'm switching to the alternate static source; be ready for an air return.'As I switched to the alternate static source; my altimeter and VSI jumped up about 200 feet and 400 FPM as I would've expected; only my airspeed didn't change. It still showed about 80 KTS. I leveled off at 3;000 feet and looked at the FO's airspeed indicator and saw that it read about 220 KTS. His altimeter; however; was still 1;000 feet higher than mine (reading 4;000 feet). I switched the static source back to normal; and then back to alternate again: both times my airspeed indicator and the FO's altimeter did not correct themselves. I told the FO 'we need to do an air return; call up ATC and advise them.' He said 'roger' and didn't key the mic. He then said 'airspeed' as we were approaching 240 KTS.I keyed the mic and advised ATC we were having an issue; and we would need to return to land at [departure airport] (for the remainder of the flight; I elected to fly and cover the radios). ATC responded with a heading change that directed us back. Additionally; they asked if I required assistance. I responded 'Negative; requesting lower altitude.' ATC then gave us altitude at our discretion.I told the FO to run the descent and approach checklists. For the remainder of the flight; I primarily used the FO's instruments in my scan; but cross-referenced with my altimeter; and the SAS indicator. As we descended to approximately 2;000 feet; the FO's altimeter corrected itself; as did my airspeed indicator. Noting our proximity to the airport; I called 'below 215; flaps 1/4;' which the FO complied with. Amidst this occurring; ATC asked if we had the field in sight (I responded affirmative); and they cleared us for the visual/told us to contact Tower. I switched over to the Tower frequency to monitor; set the aircraft up on a 2 mile final; and called 'below 175; flaps 1/2; gear down; before landing checklist.'We completed the before landing checklist; contacted clearance to land. I carried an extra 10 KTS of airspeed on final to be safe; but below 2;000 feet bothmy airspeed indicator; and the FO's altimeter seemed to have corrected their issues. I landed with the alternate static source engaged; landing was normal.After; we shut down the engines and secured the aircraft; I walked around and inspected all static ports (and pitot tubes for good measure); and noted that all ports were clear as I'd initially remembered from pre-flight. Aircraft was squawked accordingly.
SA227 Captain returned to departure airport after noting erroneous airspeed and altitude indications; probably related to a pitot/static issue.