Factors To Consider When Transitioning From Props To Jets, Part 1

While business jets offer considerable performance advantages in range and speed, there are distinct differences from a propeller aircraft that need to be mastered when a pilot steps up to jets. The higher speeds, complex systems, different aerodynamic and handling characteristics, not to mention the vast differences flying near the tropopause, require a markedly new set of knowledge and skills.  

Earning a type rating in a jet doesn’t necessarily mean proficiency and competency in jet operations. As many Designated Pilot Examiners have said at the conclusion of a practical exam, “This is a license to learn.” Following are a sample of  important differences contrasting a jet’s handling and performance from a propeller aircraft that simulator-based training curriculums don’t cover in detail.

Takeoff Differences

Let’s begin with takeoff.  According to the NTSB: “Few safety margins are included in the accelerate-stop distances. Therefore, any substandard performance by the pilots, brakes, or other airplane equipment related to the airplane acceleration or stopping performance will result in the airplane overrunning the end of the runway.”  

The good news is that a properly maintained jet engine has an exceptionally low rate of failure. Now for the reality check. A Flight Safety Foundation study on business jet safety found that 96% of the high-speed rejected takeoff incidents in the NTSB, FAA and NASA-ASRS databases were due to non-engine causes. Traffic conflicts, tire failures, master caution warning, animal strikes, loss of directional control and adverse runway conditions are the leading causes of high-speed rejected takeoff incidents recorded in those databases.

A tragic loss of tire pressure led to the fatal accident of a Bombardier Learjet 60 on Sept. 19, 2008, during a rejected takeoff at Metropolitan Airport in Columbia, South Carolina. Four of the six occupants of the jet died.

The NTSB investigation revealed that the tires had experienced approximately 2% pressure loss per day in the previous three weeks since the tire pressures had last been checked.  At the time of the accident the tire pressure was approximately 140 psi, dangerously below the recommended pressure of 219 psi.  High speed tires failures are an example in which pilots need to properly understand the maintenance and operating aspects of important systems and components on their jets. 

Be advised that the allowable center-of-gravity range tends to be narrow on business jets. Business aviation’s safety reputation suffered a setback on Feb. 2, 2005, when a Bombardier Challenger 600 blasted through the perimeter fence at the end of Teterboro Airport’s Runway 06 and crashed into the building across the street.

The NTSB determined the pilots failed to ensure the jet was loaded within weight and balance limits. When they attempted to take off, the center of gravity was well forward of the takeoff limit and the jet would not rotate. By then it had roared well past the critical takeoff decision speed.

In the real world, you will encounter situations in which an additional passenger might decide to join you. This will require you to revise the aircraft’s weight and balance, not only for takeoff, but you must check for the shift in the CG throughout the rest of the flight.

You will also be confronted with runway changes at the last minute, or perhaps an intersection takeoff clearance. Any of these changes can negate the assumptions made in your takeoff planning. You must be assured that your aircraft meets the performance requirements for the newly assigned runway length, wind components and different departure procedures, especially when adverse weather and/or terrain are present.

Stall Behavior

The wings on jets do not stall the same as propeller aircraft. The NTSB’s investigation involving the fatal crash of a Bombardier Challenger 600 near Truckee Tahoe Airport, California, in July 2021 included an important docket from the Office of Research and Engineering which described the stall characteristics of the high-performance jet to illustrate this point.  

The Challenger’s wing exhibits a “leading edge” stall, which is markedly different from the description of stalls given in private pilot ground schools. These high-performance designs produce a small bubble along the leading edge that  is inconsequential until reaching the critical angle of attack, at which point it “bursts” over the entire upper surface of the wing, especially extending outboard.

The stall occurs with no natural warning. The stall fully develops on one wing before the other wing has even begun to separate causing an abrupt and uncontrollable rolling motion. It is impossible to arrest the rolling motion until the AOA is reduced and the stalling condition removed.

Another different aerodynamic characteristic of swept wings is the spanwise flow toward the tip, especially as the AOA increases. The air flow becomes increasingly separated beginning near the wing tips and progresses inboard. Airfoil sections at the wing tips tend to be the thinnest, and thus have even sharper radius leading edges, leading to even greater susceptibility to the leading edge stall phenomena.  

The fatal accident of an Embraer Phenom 300 on Jan. 2, 2023, at Provo Municipal Airport, Utah, sadly highlights the unforgiving characteristics of high-performance jet wings with ice contamination. The pilot’s failure to deice in weather conditions conducive to ice accumulation resulted in a stall at lift-off.

Slight irregularities near the leading edge can trip the boundary layer and cause a stall at a lower AOA.  This includes wing surface contamination, deteriorated aerodynamic seals and anti-icing fluids. The Configuration Deviation Lists in some jets contain limitations due to aerodynamic seal degradation and reduce the jet’s allowed operating weights.

Simulator training doesn’t provide adequate knowledge about the aerodynamic risks of takeoffs in adverse weather. During crosswind takeoffs and landings, the aircraft is in a controlled sideslip.  

The “downwind” wing experiences the airflow at a greater angle, which decreases its lift, increases drag, promotes the span-wise flow of air, and thereby reduces its stall AOA. Flight testing has determined that sideslip reduces the stall AOA of the trailing wing from 16 deg. to 11 deg. Wind tunnel tests have determined that the stall AOA is reduced from almost 21 deg. to 15.3 deg. by anti-icing fluids. Beware that the combination of wing contamination, ground effect and crosswinds are additive at reducing the stall AOA.

In Part 2 of this article, we discuss how a jet’s handling characteristics change during high-altitude flight.