Narrative:

While on the RNAV approach for runway X at the ZZZ airport; I leveled off at the intermediate altitude of 2100 between the fixes zzzzz and ZZZZZ1; and actuated the landing gear lever. I heard and felt the landing gear extending; and ran the before landing checklist; but did not see the only down and locked green light light up. Because of this; I was not sure the gear were in fact locked in the down position. Since the light is located directly behind the long; thick arm of the common elevator control; it was hard to tell if it was lit from my angle. I proceeded to cycle the gear once; and noticed that the up red light was working; but not the down green light. The passenger seated next to me also did not see the down green light. I then quickly removed the green 'down' light; and replaced it with the red 'up' light; but it did not seem to work in the 'down' socket either; as it did in its own socket. But while I was trying to determine the extent and cause of the malfunction; I did not notice that I had drifted several hundred feet below the charted altitude. Fortunately; by this point I had broken out of the clouds and was actually in VFR conditions; about 1000 feet above the ground; and about 7 miles from the airport. I determined that the ceiling and visibility would have then allowed me to continue to operate under VFR to the airport. But since I had not been cleared for the visual; and because there was an obstruction in the area at 935 feet; I began to climb back up to the charted altitude. By the final approach fix; I decided to do the missed approach to the hold over ZZZZZ2. I informed [ATC] of the situation; so as to get assistance with my problem. I ran the gear malfunction checklist; and was informed by a passing aircraft directed there by ATC that my all my landing gear appeared to be extended. Since nearby ZZZ has an ILS approach and the appropriate fire and rescue equipment; I elected to land there and asked for them to stand by. I got vectored for the ILS X approach; and landed as softly as possible. Having the flaps fully extended; and the power at idle did not result in a gear unsafe alarm. Since the gear behaved normally; and because I did not want to stop too abruptly; and because the fire trucks were blocking the first taxiway; I slowly continued to the second taxiway and exited the active runway and into the first ramp area available. I did this because I not want to go roll too far; just in case the gear were not secure; even though my passengers wanted me to continue all the way to the FBO. I cancelled my flight plan; and answered the questions of the lead fire and rescuer. The aircraft was then towed to a service shop on the field; where new bulbs were installed; and the landing gear was tested without any malfunctions detected. The aircraft was then released for continued normal operations by the mechanic. In retrospect; I should not have tried to diagnose the malfunction while on the approach; no matter how simple the action; because this caused me to be distracted and descend below a charted altitude; which could have been disastrous. It would have been more appropriate to discontinue the descent; proceed to go missed; and then try to fix the problem. Additionally; I should just have stopped on the runway as soon as possible; and not continue to roll or turn; as the gear might have been unsafe. Also; this is an old airplane; and I would like to suggest to the FAA that they not allow aircraft of a certain age to continue to operate normally; because of archaic and non-standard equipment; metal fatigue; worn parts; loose electrical connections; and lack of modern safety equipment; such as shoulder harnesses. I feel that too many old aircraft with components about to fail; along with pilots trying to operate unusual components hodge-podged together in these old 'franken-planes;' in challenging conditions; will lead to accidents.

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Original NASA ASRS Text

Title: BE-55 pilot reported an altitude deviation while troubleshooting a gear unsafe indication. ATC reported attempting to help the BE-55 pilot.

Narrative: While on the RNAV approach for runway X at the ZZZ airport; I leveled off at the intermediate altitude of 2100 between the fixes ZZZZZ and ZZZZZ1; and actuated the landing gear lever. I heard and felt the landing gear extending; and ran the before landing checklist; but did not see the only down and locked green light light up. Because of this; I was not sure the gear were in fact locked in the down position. Since the light is located directly behind the long; thick arm of the common elevator control; it was hard to tell if it was lit from my angle. I proceeded to cycle the gear once; and noticed that the up red light was working; but not the down green light. The passenger seated next to me also did not see the down green light. I then quickly removed the green 'down' light; and replaced it with the red 'up' light; but it did not seem to work in the 'down' socket either; as it did in its own socket. But while I was trying to determine the extent and cause of the malfunction; I did not notice that I had drifted several hundred feet below the charted altitude. Fortunately; by this point I had broken out of the clouds and was actually in VFR conditions; about 1000 feet above the ground; and about 7 miles from the airport. I determined that the ceiling and visibility would have then allowed me to continue to operate under VFR to the airport. But since I had not been cleared for the visual; and because there was an obstruction in the area at 935 feet; I began to climb back up to the charted altitude. By the final approach fix; I decided to do the missed approach to the hold over ZZZZZ2. I informed [ATC] of the situation; so as to get assistance with my problem. I ran the gear malfunction checklist; and was informed by a passing aircraft directed there by ATC that my all my landing gear appeared to be extended. Since nearby ZZZ has an ILS approach and the appropriate fire and rescue equipment; I elected to land there and asked for them to stand by. I got vectored for the ILS X approach; and landed as softly as possible. Having the flaps fully extended; and the power at idle did not result in a gear unsafe alarm. Since the gear behaved normally; and because I did not want to stop too abruptly; and because the fire trucks were blocking the first taxiway; I slowly continued to the second taxiway and exited the active runway and into the first ramp area available. I did this because I not want to go roll too far; just in case the gear were not secure; even though my passengers wanted me to continue all the way to the FBO. I cancelled my flight plan; and answered the questions of the lead Fire and Rescuer. The aircraft was then towed to a service shop on the field; where new bulbs were installed; and the landing gear was tested without any malfunctions detected. The aircraft was then released for continued normal operations by the mechanic. In retrospect; I should not have tried to diagnose the malfunction while on the approach; no matter how simple the action; because this caused me to be distracted and descend below a charted altitude; which could have been disastrous. It would have been more appropriate to discontinue the descent; proceed to go missed; and then try to fix the problem. Additionally; I should just have stopped on the runway as soon as possible; and not continue to roll or turn; as the gear might have been unsafe. Also; this is an old airplane; and I would like to suggest to the FAA that they not allow aircraft of a certain age to continue to operate normally; because of archaic and non-standard equipment; metal fatigue; worn parts; loose electrical connections; and lack of modern safety equipment; such as shoulder harnesses. I feel that too many old aircraft with components about to fail; along with pilots trying to operate unusual components hodge-podged together in these old 'Franken-planes;' in challenging conditions; will lead to accidents.

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.