An altitude deviation ensued following the departure of the Captain to investigate a coffee maker and the reaction of the First Officer to apparently momentary engine parameter spikes which caused him to disconnect the autoflight systems immediately prior to reaching the programmed cruise altitude.
Synopsis
An altitude deviation ensued following the departure of the Captain to investigate a coffee maker and the reaction of the First Officer to apparently momentary engine parameter spikes which caused him to disconnect the autoflight systems immediately prior to reaching the programmed cruise altitude.
Narrative
The deviation occurred while the aircraft was in the climb phase after taking off. I was acting second in command pilot occupying the right seat in the cockpit. The aircraft was being flown on a left course deviation. All the settings were performed by the pilot in command.At some point; the Flight Attendant came to the cockpit and asked for some instructions from the pilot in command with regards to the operation of equipment in the galley. While in the climb phase; prior to level off; the pilot in command left the cockpit to help the Flight Attendant with the galley equipment. I kept on monitoring the engine and flight instruments while in the climb. After passing FL280; both engines' TGT (Turbine Gas Temperature) gauges jumped from normal operation to the very bottom of the amber arc (warning area). At this point; I disconnected the Auto Throttles and reduced the power/fuel flow so the TGT indication would come down into the normal operation range.As soon as the TGT gauges came down into normal; our right engine LP (low pressure) gauge spiked to the warning - red - zone. These deviations were momentary not lasting more than couple of seconds. The autopilot was disconnected thus preventing the aircraft from leveling off at the 30;000 FT assigned altitude. As I cross-referenced all the instruments; I noticed the altitude deviation and proceeded to correct it. According to my observations; flying the plane from the right side and after cross referencing all the instruments; the deviation was not larger than 200 FT and we did not interfere with any other aircraft either vertically or laterally.
Second reporter narrative
I left the Flight Deck with the autopilot and auto throttles on with 30;000 set in the altitude alerter. I was in the back for about 5 minutes. On my return to the Flight Deck; I experienced negative G's which I thought might be the result of the First Officer trying to get back to an assigned altitude. Upon my arrival; I observed an altitude of 30;500 FT; 30;000 set in the altitude alerter; the autopilot and auto throttles off; and a power setting that produced an airspeed close to red line. Within 2 seconds of these observations; I pulled the throttles to idle. The First Officer leveled at 30;000 FT; and engaged the autopilot and auto throttles. The remainder of the flight was normal and without any issues.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.