AINsight: Don’t Be Too Slow on the Draw during Takeoff

 - January 29, 2021, 11:45 AM

Before advancing the thrust levers of a business jet or airliner for takeoff, pilots must calculate and review performance data to ensure there is enough runway distance available and that all obstacles will be cleared while climbing up to 1,500 feet. To complicate matters, this data must account for two different scenarios: either all engines operating or one engine inoperative.

Recent incidents and accidents point to several common errors that relate to takeoff performance calculations. Crew data input errors into takeoff performance systems, flight management computers, and thrust management computers are most common. Weight entry errors ranging from 10,000 to 100,000 pounds less than actual takeoff weight produce lower than required takeoff speeds (V1, Vr, and V2). Other gotchas include selecting the wrong thrust and/or flap setting or taking off from an intersection that provides less takeoff distance than planned.

An emerging threat identified through incident investigations and flight data analysis points to handling errors by the pilot flying (PF). Lower-than-prescribed rotation rates are the lead stories in the most recent issues of Safety-First from Airbus and the ISASI Forum from the International Society of Air Safety Investigators. Both publications point out that slow rotation rates during takeoff hold the potential to “negate” takeoff performance guarantees.

To highlight this point, Airbus details an event involving an Airbus A340-300 taking off from the El Dorado International Airport in Bogota, Columbia. Bogota is challenging—it is in the Andes Mountains, sits at 8,360 feet, and has high terrain in all sectors.

In this example, the aircraft would depart from 12,467-foot-long Runway 13R with 268 passengers, 13 crewmembers, and enough fuel to fly to Paris Charles de Gaulle Airport. The actual takeoff gross weight was 236.9 tons, just under the maximum allowable takeoff weight of 237.0 tons under these conditions. Margins were thin and takeoff data called for a TOGA (max thrust) takeoff.

Flight data indicated V1 (128 knots) was reached 54 seconds after TOGA thrust was selected. The PF then began rotation close to Vr and one second later the pitch began to increase. At V2 (149 knots), the aircraft was still on the ground. Liftoff occurred at 155 knots—only 459 feet from the end of the runway. The aircraft overflew the end of the runway at six-foot radio altitude.

Further analysis revealed that aircraft acceleration was as expected, but the average rotation rate during takeoff was only 1 degree per second. Airbus A320/330/340/380 flight crew operating manuals (FCOM) and SOPs specify a 3 degree per second rotation rate. The A220 specifies a 3- to 5-degree rotation rate.

Beyond the Bogota investigation, Airbus and EASA analyzed thousands of other flights and revealed that “under rotation” during takeoff is a common occurrence.

According to certification requirements, takeoff distance (TOD) on a dry runway is calculated by taking the greatest value of either the TOD computed with one engine failure just before reaching V1, or the TOD computed with all engines operative with an additional margin of 15 percent (1.15xTOD).

On aircraft with more than two engines, such as the A340-300, the TOD is often limited based on the 1.15xTOD factor based on the loss of only a quarter (25 percent for a four-engine aircraft) of the total thrust available.

On aircraft with two engines, the TOD is often provided with the one engine failure scenario because the loss of half (50 percent) of the thrust greatly impacts the TOD. In this case, there is an additional margin for aircraft with both engines operating.

Keep in mind, these certified TODs are only valid if the rotation rate is as prescribed in the manufacturer’s FCOM/SOPs. In the case of the Bogota event, Airbus determined that a rotation rate of 2 degrees per second would equate to an additional 1,000 feet of takeoff distance. The “normal” rotation rates of 1.0 degrees per second (or less) would equate to a distance far greater than 1,000 feet. In short, this is alarming.

For operators, during training in the simulator, there is an opportunity to emphasize the importance of proper rotation rates during takeoff. Pick an airport where the aircraft is runway or climb performance limited—including SNA, BUR, and EGE—and look at the effects of slow rotation rates with all engines operating or one engine inoperative. It seems basic, but at Vr begin a positive rotation, maintain an outside visual reference to maintain the proper rotation rate and pitch, and then fly into the flight director guidance. 

Flight data analysis during routine flights suggests that lower-than-normal rotation rates are common. Anecdotally, in the business aviation community, there is a perception to rotate (takeoff) or brake (landing) for comfort. In conversations with airline crews and others, there is a belief that “milking” or “easing” the aircraft into flight during hot, heavy, or high-altitude takeoffs will enhance safety margins. In all cases, this is not correct.

According to Airbus—and ostensibly other aircraft manufacturers—“the appropriate takeoff rotation maneuver is a balance between good takeoff performance and sufficient margin versus tailstrike, stall speed, and minimum control speeds.”

Pilot, safety expert, consultant, and aviation journalist Stuart “Kipp” Lau writes about flight safety and airmanship for AIN. He can be reached at stuart.lau3@gmail.com.