Seneca I. The Seneca II also introduced optional "club seating" whereby the two center-row seats face rearwards and the two back seats face forward allowing more legroom in the passenger cabin. A total of 2,588 Seneca IIs were built. Gross weights are for takeoff and for landing, with all weight in excess of required to be fuel. PA-34-220T Seneca III In 1981, the PA-34-220T Seneca III was introduced, having completed certification on 17 December 1980. The change in model designation reflected an engine upgrade. Continental TSIO-360-KB engines were used which produced 220 horsepower (165 kW), although only rated as such for five minutes and then dropping to . The horsepower increase, with the new engines limit of 2800 rpm (up from 2575 rpm), combined for much improved climb and cruise performance. The new aircraft also incorporated a one-piece windshield and a bare metal instrument panel instead of one covered with a removable plastic fascia. Because of the raised zero-fuel weight and the raised maximum take-off weight, the Seneca III has the highest useful load of all the PA-34 variants. Some later models have electrically-actuated flaps. More than 930 Seneca IIIs were built; the last 37 Seneca IIIs built had a 28-volt electrical system rather than the 14-volt system of previous aircraft. The aircraft's gross weight was increased to for takeoff and for landing. A typical Seneca III with air conditioning and deicing equipment has a useful load of . PA-34-220T Seneca IV In 1994, the "New" Piper Aircraft company introduced the Seneca IV, having achieved certification on 17 November 1993. This model was similar to the Seneca III offering minor improvements, such as a streamlined engine cowl for increased cruise performance. It continued to use the counter-rotating Continental TSIO-360-KB engines and gross weights remained unchanged. A total of 71 Seneca IVs were built. PA-34-220T Seneca V Certified on 11 December 1996, the Seneca V was put into production as a 1997 model year. Again the cowls were redesigned for increased performance, several cockpit switches were relocated from the panel to the headliner, and an improved engine variant, the Continental TSIO-360-RB, fitted with an intercooler, was used. The Seneca V's gross weights remain the same as the Seneca III and IV at for takeoff and for landing, therefore, with all of the added features, the useful load is reduced by about . The standard useful load for the 2014 model is