Narrative:

I was flying doing low level work south of ZZZ at approximately 800 ft. AGL. After finishing several hours of this flying the in the region assigned; I was ferrying under VFR back to ZZZ1; where we had been staging out of for the past five days. While passing south of ZZZ; I made it a point to remain below 2;200 ft. MSL; to stay below the 2;600 ft. Floor of ZZZ class C airspace. I was trying to remain as high as possible due to low level turbulence; without getting too close to the lower deck of ZZZ class C space. We had seen quite a few birds during the course of our flight. While scanning a bit more than usual for birds; I was also tuning in the frequency for ZZZ1 unicom and AWOS; in preparation for performing my approach checklist. While doing this; I glanced at my altimeter and realized that I had strayed up to 2;450 ft. MSL. I immediately corrected back to 2;200 ft. When approaching ZZZ1 and setting in the current altimeter setting; I realized that I had been flying around 280 ft. Higher than my indicated altitude. This would have put me about 8-9 miles south of ZZZ at 2;730 ft. And into the ZZZ class C.contributing factors: - this was my last day of two weeks of flying this contract. Distracted by thinking about getting home. - Was doing most of my flying for almost two weeks; using my radar altimeter as my primary altitude instrument. This; due to the nature of the low level application work I was contracted to do. I had experienced a near miss with a big bird (hawk or vulture) earlier in the morning in the same area. Was keeping too much emphasis on looking outside and not on appropriately flying the plane. Inappropriate prioritizing. I thought since I was only going to be under the class C for less than 5 minutes; I could easily hold an altitude for that long; so I decided to stay a bit closer to the class C than I normally would. Complacency. I was dealing with increasing low-level turbulence on the flight - had two [passengers] on board and was trying to minimize their exposure to the low level; moderate turbulence. In reality; an extra 500 ft. Lower would not have been much different than the 2;200 ft. I decided to fly. Things to different moving forward. Lessons learned: call the local approach facility for flight following when flying near protected airspace. I had spoken to ZZZ approach several times in the past week of flying and they were always friendly and helpful. I should have taken the extra one or two minutes to establish contact with them. Give myself a greater margin around and under protected airspace. Remain vigilant to keep a current altimeter setting; even when prioritizing the use of the radar altimeter. Be more willing to use an autopilot when one is available. Remind myself that I become more vulnerable to mistakes if or when I start to 'let my guard down'; at the end of a long day.

Related reports:

Google
 

Original NASA ASRS Text

Title: BE90 Captain reported an altimeter error resulted in an airspace incursion.

Narrative: I was flying doing low level work south of ZZZ at approximately 800 ft. AGL. After finishing several hours of this flying the in the region assigned; I was ferrying under VFR back to ZZZ1; where we had been staging out of for the past five days. While passing south of ZZZ; I made it a point to remain below 2;200 ft. MSL; to stay below the 2;600 ft. floor of ZZZ Class C airspace. I was trying to remain as high as possible due to low level turbulence; without getting too close to the lower deck of ZZZ Class C space. We had seen quite a few birds during the course of our flight. While scanning a bit more than usual for birds; I was also tuning in the frequency for ZZZ1 Unicom and AWOS; in preparation for performing my approach checklist. While doing this; I glanced at my altimeter and realized that I had strayed up to 2;450 ft. MSL. I immediately corrected back to 2;200 ft. When approaching ZZZ1 and setting in the current altimeter setting; I realized that I had been flying around 280 ft. higher than my indicated altitude. This would have put me about 8-9 miles south of ZZZ at 2;730 ft. and into the ZZZ Class C.Contributing factors: - This was my last day of two weeks of flying this contract. Distracted by thinking about getting home. - Was doing most of my flying for almost two weeks; using my Radar Altimeter as my primary altitude instrument. This; due to the nature of the low level application work I was contracted to do. I had experienced a near miss with a big bird (hawk or vulture) earlier in the morning in the same area. Was keeping too much emphasis on looking outside and not on appropriately flying the plane. Inappropriate prioritizing. I thought since I was only going to be under the Class C for less than 5 minutes; I could easily hold an altitude for that long; so I decided to stay a bit closer to the Class C than I normally would. Complacency. I was dealing with increasing low-level turbulence on the flight - Had two [passengers] on board and was trying to minimize their exposure to the low level; moderate turbulence. In reality; an extra 500 ft. lower would not have been much different than the 2;200 ft. I decided to fly. Things to different moving forward. LESSONS LEARNED: Call the local approach facility for flight following when flying near protected airspace. I had spoken to ZZZ Approach several times in the past week of flying and they were always friendly and helpful. I should have taken the extra one or two minutes to establish contact with them. Give myself a greater margin around and under protected airspace. Remain vigilant to keep a current Altimeter setting; even when prioritizing the use of the Radar Altimeter. Be more willing to use an autopilot when one is available. Remind myself that I become more vulnerable to mistakes if or when I start to 'let my guard down'; at the end of a long day.

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.