Narrative:

Conducting a maintenance test flight to determine proper operation of landing gear. We needed to get the plane up above 10;000 and go fast; then bring the power up and down sharply to see if this changed hydraulic pressure or caused problem to reappear (intermittent problem had caused nose gear to come unlocked; or completely lower uncommanded). Flight was under part 91 IFR. Heavy rain. I was first officer; non-flying pilot. We departed on a round robin IFR flight plan; we were cleared for departure. Initial climb was to 3;000 feet. After checking in with approach; they climbed us to 4;000. Shortly thereafter; approach said to turn direct to [waypoint] zzzzz and maintain 250 knots. I repeated this to the controller; then looked down to the FMS boxes to set them both to go direct to zzzzz. I also turned on the weather radar at this point on both sides of the cockpit; I was heads down for a few seconds; and when I looked up we were in a steep climb. The captain (flying pilot) had dialed in 10;000 feet on the altitude selector and was climbing like a rocket (the plane was at a light weight; only about 2;500 pounds of fuel and cold conditions; so it will climb about 6;000 to 10;000 FPM easily at low altitude). I had barely enough time to get the words out of my mouth that I didn't think we were cleared above 4;000; when the controller asked what altitude we were going to because we were cleared to 4;000. The captain responded on radio at this point that he was climbing to 10;000. The controller said to level off at 9;000. There was no TCAS alert and no conflict. The flight continued as normal and we returned to base a few minutes later.I believe contributing factors were:-being distracted by monitoring gear; hydraulics because of intermittent problems on several flights before. The plane had been written up 3 of the last 4 flight legs for nose gear extending in flight; it had been repaired by 3 different shops; actuators replaced and rebuilt; switches replaced.-bad weather; strong winds and lots of bumps and ice once we got into the clouds. -The flying pilot says he 'could have sworn the controller said to climb and maintain 10;000; and maintain 250 KTS; when he only said maintain 250 KTS'. Sometimes those 2 things do go together; so I think he heard what he wanted to hear; but that is why we repeat the altitude back to the controller. In this case the controller did not say 10;000; I did not repeat back 10;000; or set 10;000 on the altitude selector. The captain set this himself and pitched to plane up while I was dealing with avionics and checklists.-I wasn't feeling pressure to get this flight done quickly; but looking back; I think the captain was in a hurry to get this flight done quickly for cost reasons; and the factory maintenance people that had just repaired the plane were waiting for us to get back. Our procedure for changing altitude is for the non-flying pilot to repeat back the altitude to the controller; set the altitude; then say the altitude again; and wait for a verbal response from the flying pilot; verifying the altitude; then the flying pilot starts climbing or descending. While I was programming the FMS; the captain skipped this; because I was overloaded with other tasks; set the altitude himself and started climbing without my knowledge.-human factors: we were both completely soaking wet from the waist down from rains; the rain was coming down sideways while fueling the plane; and this could have slowed me from catching the other pilot.

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Original NASA ASRS Text

Title: Learjet 60 First Officer reported the Captain started a climb after misunderstanding the Controller's clearance.

Narrative: Conducting a maintenance test flight to determine proper operation of landing gear. We needed to get the plane up above 10;000 and go fast; then bring the power up and down sharply to see if this changed hydraulic pressure or caused problem to reappear (intermittent problem had caused nose gear to come unlocked; or completely lower uncommanded). Flight was under Part 91 IFR. Heavy rain. I was First Officer; non-flying pilot. We departed on a round robin IFR flight plan; we were cleared for departure. Initial climb was to 3;000 feet. After checking in with approach; they climbed us to 4;000. Shortly thereafter; approach said to turn direct to [waypoint] ZZZZZ and maintain 250 knots. I repeated this to the controller; then looked down to the FMS boxes to set them both to go direct to ZZZZZ. I also turned on the weather radar at this point on both sides of the cockpit; I was heads down for a few seconds; and when I looked up we were in a steep climb. The Captain (flying pilot) had dialed in 10;000 feet on the altitude selector and was climbing like a rocket (the plane was at a light weight; only about 2;500 LBS of fuel and cold conditions; so it will climb about 6;000 to 10;000 FPM easily at low altitude). I had barely enough time to get the words out of my mouth that I didn't think we were cleared above 4;000; when the Controller asked what altitude we were going to because we were cleared to 4;000. The Captain responded on radio at this point that he was climbing to 10;000. The Controller said to level off at 9;000. There was no TCAS alert and no conflict. The flight continued as normal and we returned to base a few minutes later.I believe contributing factors were:-Being distracted by monitoring gear; hydraulics because of intermittent problems on several flights before. The plane had been written up 3 of the last 4 flight legs for nose gear extending in flight; it had been repaired by 3 different shops; actuators replaced and rebuilt; switches replaced.-Bad weather; strong winds and lots of bumps and ice once we got into the clouds. -The flying pilot says he 'could have sworn the controller said to climb and maintain 10;000; and maintain 250 KTS; when he only said maintain 250 KTS'. Sometimes those 2 things do go together; so I think he heard what he wanted to hear; but that is why we repeat the altitude back to the Controller. In this case the Controller did not say 10;000; I did not repeat back 10;000; or set 10;000 on the altitude selector. The Captain set this himself and pitched to plane up while I was dealing with avionics and checklists.-I wasn't feeling pressure to get this flight done quickly; but looking back; I think the Captain was in a hurry to get this flight done quickly for cost reasons; and the factory maintenance people that had just repaired the plane were waiting for us to get back. Our procedure for changing altitude is for the non-flying pilot to repeat back the altitude to the controller; set the altitude; then say the altitude again; and wait for a verbal response from the flying pilot; verifying the altitude; then the flying pilot starts climbing or descending. While I was programming the FMS; the Captain skipped this; because I was overloaded with other tasks; set the altitude himself and started climbing without my knowledge.-Human factors: we were both completely soaking wet from the waist down from rains; the rain was coming down sideways while fueling the plane; and this could have slowed me from catching the other pilot.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.