Human Factors Design Considerations for PLJs


Personal Light Jets (PLJ’s) were conceived and developed in the mid-2000’s as a more affordable type of privately owned Business Jet. PLJ’s were considered to be ‘the next step up’ for owners of light aircraft who wanted to fly a jet rather than be limited to just piston aircraft. Because the majority of these owners would only hold a Private Pilot’s Licence (as opposed to the typical credentials of a Commercial Pilot’s Licence or Airline Transport Pilot’s Licence for those flying jet aircraft) several Human Factors considerations were analysed in the design phases of these jets.


For a pilot who is transitioning from a piston-engined aircraft to a jet, one of the most noticeable differences between the two aircraft types is speed. During the design of PLJ’s, it was up to the engineers to make sure that their concepts addressed the fact that most pilots would not initially be used to flying a jet aircraft.

One of the most obvious factors that required attention was the increase of the aircraft’s airspeed. A Cirrus SR22 has a maximum cruise speed of 185 knots, compared with 300 knots for the Cirrus Vision Jet, and there is also a noticeable difference in take-off speeds between the two aircraft. In the air, the higher airspeed means that other aircraft and stationary objects such as mountains, tree tops and runways will all approach much faster. This increases the risk of having a mid-air collision or near-miss incident for a private pilot that is not used to the faster flying speed. Engineers used a combination of technology and basic design concepts to address this risk. Terrain avoidance and traffic awareness systems were incorporated into the avionic suite so that the pilot had additional warning mechanisms if they came too close to other objects. Engineers also designed maximum areas of visibility through the windscreen and allowed maximum seat adjustability so that the pilot could adjust their seats to give optimal vision of the external flight environment.

Operational characteristics, such as the engine start up sequence, also tend to be a lot faster on a jet aircraft. Because of this, there is a chance that critical parameters, such as maximum Exhaust Gas Temperature (EGT) and maximum engine RPM, may be missed by the pilot. If any of these parameters are exceeded there is a possibility that significant damage may have been caused to critical engine components which could bring about engine failure during flight. To prevent this type of damage being done, the engines in PLJ’s incorporate the latest Full Authority Digital Engine Control (FADEC) technology. This technology allows the engine to control its own system operating parameters, including the start up sequence and is able to shut the engine down if any of the critical parameters are exceeded. Incorporating this technology into PLJ’s allows a new pilot time to gain experience with the increased speed of a jet engine with minimal risk of damage.

Glass Cockpits

Initially, one aspect that was of some concern to design engineers was the concept of the glass cockpit. During the early stages of conceptual design of PLJ’s, glass-cockpits were only available in new commercial airliners and military aircraft, making flying with them unfamiliar to most private pilots. The challenge that engineers, interior designers and human factors consultants faced was that glass-cockpits provided many benefits over traditional gauges, but they also had some disadvantages. The main advantage of using glass-cockpits is their ability to substantially reduce pilot workload which then allows an improvement in working memory and cognitive processing functions.

SR-71_flight_instruments.triddle.jpg Hondajet_Cockpit_2011.jpg
Analog Cockpit Gauges (image embedded from Wikipedia on August 14, 2011) Glass Cockpit (image embedded from Wikipedia on August 14, 2011)

The downside to glass-cockpits was that there had been indications that some pilots had become over-reliant on the technology. Instead of using basic airmanship to maintain situational awareness, they were relying on the aircraft’s advanced systems to take over basic piloting skills, for example relying on a Global Positioning System as the only navigation tool and Synthetic Vision as the only way of monitoring the external environment. When trying to decide the final cockpit design and technology configuration of PLJ’s the challenge was to find a solution that negated the disadvantages of glass-cockpits, especially for single-pilot-operated flights, which most were expected to be. However, as time has progressed and glass-cockpit technology has became cheaper and more commonplace, especially in general aviation and training aircraft, glass-cockpits being the only option in a PLJ has become far less of a problem.


Noise is one of the biggest problems for PLJ’s. The main reason for this is that because of the general size of the aircraft the engine is located in close proximity to the pilots and passengers. Noise is a major contributing factor in adverse working environments, and can significantly affect a pilot, especially on long flights. Unfortunately the design constraints of PLJ’s – that is, the philosophy behind their creation of being an affordable and light-weight aircraft - means that the noise problem is not easy for engineers to solve. The current state of aircraft insulation technology means that highly effective insulation is expensive and more cost effective options are heavy and bulky. However, testing to date has proven that pressurisation of the aircraft has helped to reduce some of the noise levels in the cockpit.

Flight Testing

The aircraft designers and engineers work closely with the flight test pilots when developing PLJ’s. Flight testing is carried out by highly qualified and experienced flight test pilots, and every flight they conduct evaluates the handling characteristics of the aircraft and its systems. One of the most important criteria they report on is whether the aircraft’s capabilities match the capabilities of private pilots.

(Video embedded from YouTube on August 14, 2011) (Video embedded from YouTube on August 14, 2011)
Green, R.G., Muir, H., James, M., Gradwell, D., & Green, R.L. (1991). Human factors for pilots. Aldershot, UK: Ashgate, 1991.

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