Narrative:

I was operating my stemme glider on an IFR plan under VFR conditions under the auspices of an LOA with center. We had been assigned a block altitude FL180 - 220. We were flying in classic mountain wave conditions along the mountain range. As we approached the ceiling of our block; both my copilot and I assessed our altitude; decided that we could climb a further 800 ft and so lowered the nose slightly. The climb rate reduced and we stopped climbing at what we read as 21700 ft with the altimeter set to 29.92. A moment later; we both reacted with surprise as we realized that the actual altimeter reading was 22700 ft. At that time we could not understand how we had both misread the altimeter; however I immediately took steps to return to our assigned block altitude. Only later in the flight did I discover the reason for our error. In the vicinity of 22200 ft; the three hands of the altimeter are all pointed at the 2; and the smaller hands are obscured. Later in the flight; the wave had strengthened and we had difficulty remaining below the ceiling of our block - still at FL220. The challenge was that at that altitude; vne is significantly lower than the 145 kt red line. As a result; lowering the nose is generally not an option. Having exceeded the assigned altitude earlier; I requested and obtained an extended block ceiling to FL230. That provided enough buffer to enable us to shift the flight path laterally and so move to a weaker portion of the wave. We did not receive any comment about the deviation.conclusions: 1. An altimeter with a digital readout is probably worth the investment when flight into the flight levels is frequent. 2. Some instruction about how to avoid misreading non-digital altimeters would be appropriate for pilots intending on flying in class a airspace. I shall pass this lesson on to my flying community and also to instructors who teach at glider wave camps.

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Original NASA ASRS Text

Title: Motor glider pilot reported overshooting block altitude ceiling due to thermal activity and misreading the aircraft altimeter.

Narrative: I was operating my Stemme glider on an IFR plan under VFR conditions under the auspices of an LOA with Center. We had been assigned a block altitude FL180 - 220. We were flying in classic mountain wave conditions along the mountain range. As we approached the ceiling of our block; both my copilot and I assessed our altitude; decided that we could climb a further 800 ft and so lowered the nose slightly. The climb rate reduced and we stopped climbing at what we read as 21700 ft with the altimeter set to 29.92. A moment later; we both reacted with surprise as we realized that the actual altimeter reading was 22700 ft. At that time we could not understand how we had both misread the altimeter; however I immediately took steps to return to our assigned block altitude. Only later in the flight did I discover the reason for our error. In the vicinity of 22200 ft; the three hands of the altimeter are all pointed at the 2; and the smaller hands are obscured. Later in the flight; the wave had strengthened and we had difficulty remaining below the ceiling of our block - still at FL220. The challenge was that at that altitude; Vne is significantly lower than the 145 kt red line. As a result; lowering the nose is generally not an option. Having exceeded the assigned altitude earlier; I requested and obtained an extended block ceiling to FL230. That provided enough buffer to enable us to shift the flight path laterally and so move to a weaker portion of the wave. We did not receive any comment about the deviation.Conclusions: 1. An altimeter with a digital readout is probably worth the investment when flight into the Flight Levels is frequent. 2. Some instruction about how to avoid misreading non-digital altimeters would be appropriate for pilots intending on flying in Class A airspace. I shall pass this lesson on to my flying community and also to instructors who teach at glider wave camps.

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.