SF 340B
Flight Crew Commercial
Aircraft Equipment Problem Critical
Aircraft Equipment Problem Dissipated; Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft
While en route and leveling at 8;000 FT I called for the cruise checklist. The Captain (pilot not flying) set the propeller RPM to 1230 and found my power setting to be 72%. As I reached to adjust the power setting I noticed a sudden fluctuation of approximately 20 degrees Celsius on the right ITT [Inlet Turbine Temperature] gauge. This fluctuation would occur for approximately 10-15 seconds; stabilize for a period; and then occur again. This repeated for the next few minutes. Immediately upon noticing I brought it to the attention of the Captain. We continued and monitored for a few minutes and realized that it was continuing to occur.At this time we discussed our options; which was to continue to our destination or return to our departure airport. According to our latest weather briefing both airports weather were relatively the same and would require an ILS. We came to the conclusion that our departure airport was the more suitable airport as it had multiple approaches; did not require crossing mountains; and had better ATC; emergency; and maintenance services. About this time the ITT fluctuations had steadied; but the right ITT was approximately 50C warmer than the left engine. From my training I was aware a difference of greater that 30C could be a sign of imminent engine failure. We reviewed the Saab QRH for ITT Delta T shift; but felt it gave little guidance except to avoid specific Ng ranges. We notified ATC that we would like to return to our departure airport and they cleared us to the airport and descended us to 6;000 FT. We began our turn back and at this point we identified a useable alternate airport; immediately ahead. We then decided that this was our most suitable airport as it would allow for a timely descent with a visual approach. It was also an airport with company operations that we had both been to. We notified ATC that we would like to go to the alternate airport and they gave us a heading for the downwind Runway 3. ATC asked if we were declaring emergency but we felt this was a precautionary situation and not an emergency. The Captain then attempted to contact the company on ARINC; but was unable due to altitude. He then notified the Flight Attendant and passengers of the situation and that we were diverting to the alternate airport to make a precautionary landing. Lastly he contacted the alternate airport operations and told them to contact the company that we were diverting due to our ITT issues. We then executed a normal visual approach; landing and taxi.After the incident; we realized we did not have landing data or NOTAMs for our alternate. After discussing with the Captain we felt that though we did not have landing data; our decision was still proper as we both have experience at the alternate and know that the Saab can legally land there. We also did not want to climb (higher power settings) to get in contact with ARINC or spend time relaying information through operations in order to get our performance data. Especially if we were unsure if our situation was going to continue to degrade; we also felt that pertinent NOTAMs (outages; closures; etc.) for the alternate would be relayed to us from ATCNeither of us were able to come to a conclusion why the event was occurring. In the air; I could only come up with two scenarios. ITT trimming had gone bad on the right engine; or possibly FOD ingestion on taxi or takeoff. From my knowledge I believe ITT trimming only results in a 5-10 degree change in ITT temps and not a 20-50. Also from my experience at our departure airport; I have seen numerous FOD in movement areas consisting of paper and other trash; so I thought this was a more feasible possibility. I am still unsure why the event occurred.
A Saab 340 flight crew; confronted with varying ITT readings opted to divert to the nearest suitable airport.