Twin piston aircraft tend to be suitable for the short haul charter sector with a target market of three to eight passengers. They also appeal to the safety-conscious as well as those looking for a modest capital investment. Many owners prefer to have an aircraft that has the capability to fly to an alternative airport in the unlikely event of an engine failure. Charter flights can often also be conducted both at night or in poor weather conditions.

But single-engined aircraft are much more economical to operate and turboprops are much more capable and easier to fuel so there is little incentive for manufacturers to keep producing twin pistons. Ensuring a supply of AVGAS in regions such as Eastern Europe can also pose problems.

Although the overall numbers are reducing there are a wide variety of multi-engine pistons operating for private, corporate and charter owners in Europe. Many are used for pilot training but significant numbers are used for business and pleasure.

The PA34 Seneca tends to be a three-passenger aircraft while the Beechcraft Baron, one of the most popular light twins ever produced, is often favoured by executives for business travel and accommodates up to five passengers. The Piper Aerostar also tends to be used for between two and five passengers or up to 450 kg of freight. The sector contains a spread of Cessnas including the 310 which takes between two and five passengers with the 401 having a similar capability allied to a wider and more comfortable cabin. The 402 is more popular with groups of six to eight and the 404 Titan can accommodate up to ten.

Among its rivals are the Piper Chieftain which ferries eight passengers and can operate from many remote airstrips while the Diamond Twin Star is a popular training aircraft. For some charter operators twin pistons are part of a diversified fleet that also focuses on turboprops and may be considering adding jets.

Poland's Ad Astra Executive Charter has added a Beechcraft Baron G58 to its fleet but is has also brought a second, factory new Beechcraft 90 Gti into service. "Our goal is to become the biggest business turboprop operator in Eastern Europe," according to the company's Dorota Kowalska. The AOC fleet also offers a Beechcraft B200GT while the flight training side relies on the Diamond DA-20 Eclipse, the Cessna C172S G1000 and the Diamond DA-42 Twin Star.

The company says: "We're flying taxi, so we fly where the need is. From Norway to Malta, from Madeira to Moscow. Our clients order flights for business trips as well as family vacations."

The company says it likes to provide alternatives to jets that are more economical and can operate from unpaved and short runways that are found at the many small airports. There is a need to recruit pilots but the requirements are high, particularly in terms of time logged, because of single pilot operational requirements.

Ad Astra Executive Charter, formed a year ago as daughter company of Aviation Asset Management, a multi-purpose aviation business, reports that growing demand is forcing it to enlarge its fleet but that expansion is focusing on turboprops and possibly a small jet in 2010 rather than piston aircraft.

Cessna has produced a number of twin pistons and some of the older models have been reclaimed and adapted for useful income-generating work.

Ulfar Henningsson's Icelandic company Gardaflug Inc has owned a Cessna 337G since 1988. He recalls: "It was purchased in New Jersey in the US in poor condition and needed a huge amount of work before it was ferried to Iceland as it had been standing still for three years. During my ownership it has undergone the replacement of many parts and it has also benefited from extensive renovation work involving avionics, a new interior, cabin sound-proofing, engine overhaul and bubble windows." Henningsson says this names "just a few" improvements.

The 337G was originally purchased to carry out an ocean bird survey between Iceland and Greenland and also conduct inland surveys for birds and reindeer. "It is equipped with a photo hatch and we have done some vertical photography of cliffs and nesting areas," Henningsson explains.

The 337G's strength and attractions include its high wing construction and easy manoeuvrability, giving the photographer a clear view out the side window with the wing behind. The aircraft is exclusively used for all kinds of aerial survey charter.

Henningsson says: "The maintenance has been extensive, but since our period of operation is only May through September we have ample time to work on the aeroplane, but you have to maintain a high standard and do preventive maintenance in order to be content with owning and operating a Skymaster. Still there is little difficulty in finding spare parts. Yingling Aviation has proven an excellent source in the past and still is. But what has changed drastically is the pricing of spare parts and that has increased beyond all reason."

Henningsson warns: "To be happy with the dispatch rate you have to be on your toes in fixing everything that comes up, right away. We have not had any major difficulties as the aircraft is made ready over the winter months. The performance is much like with any light twin, manoeuvrability is vastly enhanced due to the Centreline thrust, and in low level aerial survey at slow speed the long range tanks have provided more than nine hours of endurance."

Although Avgas is only available at a few locations, and sometimes not at major airports, there has not been any fuel supply problem. "However, when operating in Greenland you have to plan well ahead since Avgas is only available in very few locations and is very expensive," Henningsson says.

He says he is biased in favour of the aircraft having owned and flown the Skymaster for over 20 years. "I find it hard to mention any drawbacks but the maintenance issues have sometimes been bothersome. It is a very safe aircraft to operate and is very much appreciated by my customers. I plan on owning and operating it for years to come." Scotland's Loganair can make sure there are no maintenance or spare parts problems. It carries out its own maintenance on both its Islanders at a purpose-run facility in Kirkwall, Orkney, and, over the years the airline has built up a very significant spare parts holding.

Loganair introduced the Islander into service in 1966 and the two aircraft that the airline now fly joined the fleet in the early 1990s.

Commercial director Jonathan Hinkles says: "We do operate some ad hoc charters with the aircraft in Orkney, although primarily within the Orkney Islands and up to Fair Isle. We are interested in ad hoc operations in this arena, although we wouldn't really seek ad hoc work which could not be serviced from our Kirkwall base. We operate quite a number of flights for organisations such as utility providers, who need to take staff out to the smaller islands."

He adds: "We have been undertaking charters up to Fair Isle to carry construction workers building the new bird observatory there and during the winter we operate a dedicated freight charter with the Islander each week to North Ronaldsay to carry perishable foodstuffs to the island. It does not have a pier capable of accommodating roll-on, roll-off ferries and during the winter the sea state often means that the air service is the only practical way of guaranteeing food supplies to the 75 island residents. This operates in addition to the three daily scheduled passenger flights from Kirkwall to North Ronaldsay."

But Loganair's capacity for ad hoc charter is limited by the two aircraft's primary commitment to operations on behalf of the Orkney Islands Council. Hinkles says: "We carry around 20,000 passengers per year on this operation and it is one of the longest-standing Islander operations in the world. Much of the downtime within the schedule is required for planned maintenance and so those ad hoc charters that we undertake have to fit around these two requirements. Most of the ad hoc charter activity - such as the utility company flights - is an extension of the social obligations which arise from the main operation in Orkney in any case."

The aircraft are therefore mainly used on Loganair's Orkney-inter-island schedule, which is a Public Service Obligation (PSO) contract and includes the world's shortest scheduled flight (at two minutes) between Westray and Papa Westray.

Additionally, Loganair will be operating extra flights this winter due to a ferry being away on refit and the consequent need to still get children across to school between the islands each day.

The maintenance facility is operated by Loganair under its EASA 145 approval. Historically, Loganair had a larger fleet of Islander aircraft and so it was fully utilised carrying out maintenance for the Loganair fleet, but following the closure of Loganair's air ambulance operations in 2006, the fleet size has reduced.

Hinkles says: "As a consequence of this, we now have some spare capacity in Kirkwall and are actively discussing the opportunities to carry out third party maintenance work including 150 and 300 hour checks and SB190 inspections with a number of other Islander owners and operators."

The Islanders use Avgas but Hinkles says: "As things stand, we have no ongoing fuel supply issues with Kirkwall. Our main issue is that the cost of aviation fuel (both Avgas and Jet A-1) in the Highlands and Islands is very high and has increased disproportionately to the fluctuations in world jet fuel prices. Supply itself is not a problem."

Peter Johnson is another respondent happy with the BN-2 Islander. Johnson, who operates a BN2B-26 says he is satisfied with the maintenance support and value and very satisfied with the dispatch reliability and operating capability. "The best aspect is the STOL capability but the worst thing is that water leaks into the cabin.

AirMed, based at Oxford airport, owns and operates four multi-engine piston aircraft. This includes two Piper Seneca III's and two Piper Chieftains. Pistons make up nearly half of AirMed's fleet of nine aircraft which includes a further four Piper Aircraft (turboprops) and the Learjet 35A.

The piston fleet is multi-role with their main function being air ambulance. However all of the aircraft can be reconfigured to be used as passenger and cargo aircraft. One of the Senecas has also been modified to allow its use as an aerial photography and survey aircraft.

"Our piston fleet plays a vital role within AirMed" says Jane Topliss, the marketing manager. "They provide our clients with the best possible choice and ensure that the most cost effective aircraft is provided for the job. This may be a Seneca for the smaller local airfields like Bembridge, or the Chieftain for eight passengers on a trip to the continent."

The smaller and more cost effective aircraft like the Senecas and Chieftains are crucial to the business aviation and medical repatriation industry, according to AirMed. "If the option of using this type of aircraft was removed then many of the less urgent medical repatriations or passenger flights would either simply not happen or would become extremely expensive. We also find it a fantastic way of introducing passengers to the benefits of business travel. Many clients who first fly in our Seneca migrate in time to our larger aircraft for their longer distance requirements."

AirMed Engineering, the maintenance arm of AirMed, not only maintains its entire Piper fleet at its EASA 145 Part M approved Oxford facilities, it also offers third party maintenance and holds a large store of spares and parts for Piper and Cessna. More recently it has also become an approved maintenance and parts supplier for the turboprop Cessna 208s. "AirMed Engineering continues to work on broadening its third party maintenance activities," says Topliss.

The Cessna 300 and Cessna 400 series bring praise for low operating costs. Giora Oren of Oren Aviation & Tech says he is very satisfied with the maintenance support and dispatch reliability and satisfied with the operating capability and value. "The best things is the speed and low consumption of fuel and the most desirable upgrade is a diesel engine," he says.

Norbert Amberger says that the C421C is a good short range aircraft and he is satisfied with the maintenance support and dispatch reliability and very satisfied with the value. He says: "The best thing is the low operating cost and the worst aspect is that the Avgas situation in Eastern Europe is bad." However, he reports that the aircraft's low-cost operation is bringing in growing business.

Another respondent says he is very satisfied with the maintenance support and dispatch reliability of the C421 Golden Eagle. He is also satisfied with the operating capability and value. "The best thing is that the aircraft is spacious and quiet and the worst thing is the toilet," he adds. "The most desirable upgrade is a digital fuel management system."

Capital Air Charter has been operating Piper Chieftain aircraft since the company was launched in 1991. The company's Lisa Humphries says: "Today we own and operate six of them along with one King Air 200 and one Blackhawk-modified King Air 200. Although the King Airs are our flagship especially with the sexy Blackhawk machine we wouldn't be here today if it were not for the versatility of our Chieftains, which have proved to be the backbone of the company. They are good solid workhorses and cater very well for our freight contracts, air ambulance contracts and they also offer affordable air taxi flights. We have the capacity to equip them with cargo nets and offer them for freight purposes especially as they all have cargo and crew doors. Air ambulance is also easy as we offer them with Lifeport stretchers and we also have the executive fit with leather seats for the charters."

Humphries asks: "How many types of aircraft can fulfill all of those roles today? I believe we are the largest Chieftain operator in Europe and still see them as part of our future as we grow into other markets."

The Diamond Twin Star also has its fans. Stuart Cook says he is very satisfied with the maintenance support. "I use Bristol Flying Centre who are excellent." he adds: "I decided not to use Diamond at Gamston as they have under-invested to support the number of aircraft sold in the last few years" He is also satisfied with the value and very satisfied with the dispatch reliability and operating capability. Cook adds: "The best thing is the economy and the worst thing was Thielert going bust and not honouring the warranty." The most desirable upgrade, he adds, would be more powerful engines. "It is a fabulous private owner aircraft which is an absolute pleasure to fly."

Another respondent says he is satisfied with the maintenance support, dispatch reliability and value and very satisfied with the operating capability. The best aspect, he adds, includes the fuel efficiency but he says the worst aspect is the maintenance costs for the Thielert engines and long range tanks are a desirable upgrade.

Allan Krintel of CB Data is a fan of the Partenavia P.68B. He is satisfied with the maintenance support and dispatch reliability and very satisfied with the operating capability and value. Krintel adds: "The best thing is that it is very good for short fields and easy to handle in most situations. The worst thing is that it is not good in icy conditions."

Chris Evans of Fantasy Foods says he is unhappy with the maintenance support for the P.68B. "Airframe parts can take a long time to obtain," he says. But he adds: "The aircraft has been operated since 1988 and the reliability is excellent." Evans is satisfied with the operating capability and value and very satisfied with the dispatch rate. The best aspect, he says, is the handling but the worst thing is icing and the most desirable upgrade is turbo charging.

There is a high degree of satisfaction with the Piper twin piston series. One company, which has two Piper Aztecs permanently out on contract, says it is very satisfied with the maintenance support, dispatch reliability, operating capability and value.

Rene Jorgensen of Dane Swede Aviation is satisfied with the maintenance support, dispatch reliability, operating capability and value of the PA31-325CR.

Kurt Bjerneby says the PA34 is a "good compromise for the owner/ pilot operating up to 500 nm." He is satisfied with the maintenance support. "There is good support from our workshop which often has spares in stock," he says. "Long experience of the aircraft type and proofed components for many years gives good dispatch reliability. Additionally our aircraft are well IFR equipped and give good operation capability year round on short runways"

Bjerneby likes the good performance, load capability and service performance IFR. He says they are good workhorses.

But Capt Armand G Baccala of Stiftung, Franz und Erika Gribi says maintenance support for the PA-34-220T is too expensive and he is not happy with the value. However he is very satisfied with the dispatch reliability and satisfied with the operating capability. "It is ideal for CPL/IR/IMC training but the suction pumps and magneto-clutches have too short a life and the TBO is too short," he adds. The most desirable upgrade, he says are "glass avionics or trading up to a light turboprop."

Carl-Gustaf Werner of Lidingo Bilcenter AB says the PA-310 and PA-31-350 give maintenance support problems. "It is hard to find an experienced technician," he says.

But the dispatch reliability is satisfactory and the aircraft is a good workhorse although icy conditions can be a problem. "The aircraft is definitely cheaper to operate than a turboprop and the lack of performance doesn't matter so much on shorter flights," he observes. The best aspect is the total cost of operation and the worst aspect the technical support. Werner would like a vortex kit upgrade.

Leigh Westwood of Air Jota Ltd says he is satisfied with the maintenance support, dispatch reliability, operating capability and value of the PA31-310 Navajo. "It is a good utility aircraft covering a wide range of uses but the the crew and cargo door could fit together better," he says.

Twin pistons have an established niche as cost-effective short haul aircraft and there is regret that manufacturers no longer have much incentive to develop new types. They are economic to operate but their age is slowly curtailing widespread use.