MBB Bo 105 Bo 105P (PAH-1)

The Bo 105P grew out of a two-step decision by the Bundeswehr. In 1974 the German Army ordered the Bo 105 as a light liaison and observation helicopter (the future M or VBH version) and in 1975, after four years of evaluation by the Heeresflieger and a number of design changes, it also selected the type as its first-generation anti-tank helicopter. Development of that version, named PAH-1 (Panzerabwehrhubschrauber 1), was completed in 1977. A total of 212 PAH-1s were delivered to the army aviation units, alongside 100 VBH liaison helicopters. In October 1979 the Spanish magazine Defensa described the planned organisation of the fleet: three regiments of 56 aircraft each, within a perspective of some 220 Bo 105s also devoted to reconnaissance and liaison.

The programme's philosophy was a compromise between complexity and cost: instead of a dedicated attack helicopter, six HOT missiles were adapted to an existing design, so that a single basic type could cover liaison and anti-tank missions. The PAH-1 has a strengthened airframe, but its avionics and dynamic system are those of the Bo 105M, with the addition of a Singer AN/ASN-129 Doppler radar. Its main armament is the Franco-German wire-guided HOT anti-tank missile, three of which are carried on each side in horizontally arranged launch tubes. HOT stands for High subsonic Optical Tube-launched: a second-generation missile weighing thirty-two kilograms, with an effective range of four kilometres and a speed of 260 metres per second. All the guidance and tracking electronics are fitted to an equipment rack in the rear of the main cabin, and aiming is done with the gyro-stabilised SFIM APX M397 sight, mounted directly on the cabin roof above the commander, who looks through a relay-lens optical system offering 3.2x and 10.8x magnification.

Power comes from two Allison 250-C20B turboshafts with a take-off rating of 400 shp each. Between 1979 and 1983 MTU built this engine version in Germany for the military variant of the Bo 105; after Rolls-Royce acquired Allison in 1995 the engine became known as the M250.

Operational tactics exploited the aircraft's outstanding manoeuvrability for swarm flight close to the ground. The rigid rotor allowed highly agile manoeuvres with only small control inputs. The approach to the operating area was usually flown in formation through forest clearings, trying to remain undetected for as long as possible; before the engagement the PAH moved into a forward assembly area where it could be refuelled under field conditions. With 560 litres of kerosene the helicopter had a maximum combat radius of around 230 kilometres, equivalent to two flying hours. After a hit, the PAH dived back behind the terrain screen to the assembly area to refuel and rearm; army aviation doctrine foresaw a swarm of PAHs engaging enemy tanks across a front of about five kilometres.

As early as 1982 plans were made for a mid-life upgrade (Kampfwertsteigerung) of the PAH-1, for which the contract was finally awarded in 1986; as a short-term measure, AN/APR-39 radar warning receivers were installed in 1983. The resulting version, designated PAH-1A1, reached the units in a conversion phase starting in 1991 and is recognisable from outside by its stepped HOT launch racks. The upgrade digitised the guidance computer, the control unit and the rack actuators, which made the commander's work easier and simplified fault analysis for maintenance crews. A modified intake protection (MELS) was fitted ahead of the air intakes, the front engine cowlings were changed, the engine oil cooling was reworked and rotor blades with roughly 10% more performance, recognisable by their rounded tips, were installed; with the A1 the missile became the HOT-2. Two further developments never left the drawing board: the BSH-1 escort version armed with Stinger air-to-air missiles, and the PAH-1 Phase 2 with an infra-red roof-mounted sight for night attacks with HOT-2; both were cancelled in 1993 as a consequence of the collapse of the Warsaw Pact.

The PAH-1A1 was replaced by 2013 by the Eurocopter Tiger, originally designated PAH-2. At the end of August 2013, during exercise Griffin Strike at the Artillery School in Idar-Oberstein, Bundeswehr Bo 105s fired a live HOT missile for the last time before the type was finally withdrawn. Part of the fleet found a second life: since the Bo 105M had been retired in 2004 and the PAHs still in service had fewer flying hours, Eurocopter converted 67 of them into VBH liaison helicopters between 2006 and 2014 by removing the weapon system and refitting the rear bench seat, under the new designation Bo 105 P1M; these flew until the end of 2016 at the International Helicopter Training Centre in Celle. Twelve more German Army Bo 105s, overhauled and remarketed by Eurocopter as the Bo 105E-4, were donated to Albania: the first flew on 25 January 2007 and the first two landed in Tirana on 24 April that year.

The PAH-1 concept was mirrored in Spain: the ATH version (Anti-Tank Helicopter, designation HA.15) of the FAMET, assembled by CASA at Getafe, carried the same three HOT launch tubes on each side of the fuselage and was the most numerous of the three Spanish versions. An anti-tank example has been preserved in the gardens of the Museo del Ejército in Toledo since 1 July 2016.