Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Multiengine
Flight Crew Last 90 Days 20; Flight Crew Total 2300; Flight Crew Type 150
Situational Awareness; Confusion
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Weather; Human Factors; Chart Or Publication
Was cleared for the VOR Rwy 04 approach to PIE. This was my first time flying this approach. Approach was dialed into GPS though this is not a GPS overlap approach. VLOC was enabled on GPS. Was using government approach plate. There is no FAF on this approach but there is a step down fix at 3.5 DME called JULSO. GPS provided a fix called FF04 with a distance. I know that GPS approaches need a pseudo fix when there is no designated final approach fix but this was not a GPS approach. I falsely assumed that FF04 was referencing the PIE vortac which is the IAF and MAP. Thus when the GPS distance to FF04 dropped to 3.5 I started my descent to the MDA assuming I was at JULSO. The display I was using on the GPS was one that did not show a moving map but rather time/distance/xtrack/GS/pseudo CDI so I did not have a way to visually confirm I was at JULSO. Tower advised me of an altitude alert. I was at 500 feet which is above minimums when past JULSO. Unfortunately; I was not past JULSO. Fortunately; I was VFR once below 1200 feet so there was no danger of collision with terrain or manmade objects. When advised of the altitude alert I switched to my flight plan page and saw JULSO in the sequence. By this time I was then at JULSO and proceeded with the landing as usual. Since this was not a GPS approach I am still perplexed why the GPS includes a pseudo fix and why it simply did not reference JULSO or PIE VORTAC. I do not use Jeppesen approach plates but I am told they show the pseudo fixes on the approach plates. Had this pseudo fix been shown on my government approach plate it would have eliminated all the confusion. I am trying to access a Jeppesen approach plate for the PIE VOR Rwy 04 approach to see if indeed they show FF04 on it since again; this was not a GPS approach.
While flying a VOR approach in VMC conditions; GA pilot misinterpreted the GPS approach presentation and descended early. This resulted in flight below minimum altitude for that location and subsequent ATC altitude alert call. By the time the radio call for the altitude alert was completed; the aircraft was inside the FAF and at a safe altitude.