Once you’ve watched a professional flight crew fly a business jet equipped with Safe Flight’s AutoPower autothrottle system, you’ll wonder why autothrottles aren’t standard on more airplanes. While they offer efficiency and passenger comfort benefits, it’s the safety aspects that make autothrottles well worthwhile.
While it may seem as if autothrottles are a relatively new technology, Safe Flight pioneered the devices with installations in a DC-3 and a Beech 18 in the 1950s. The company’s first jet applications were in airliners in the 1960s, and the first business aviation autothrottles were Safe Flight’s King Air and Gulfstream II systems in the 1970s. Now the company has accomplished more than 9,000 autothrottle installations in more than 40 aircraft types, the latest of which are the Gulfstream G200, Hawker 800/900, Bombardier Challenger 604/605 and Challenger 850/CRJ200 and Cessna Citation X (for retrofit, not the new X, which has Garmin autothrottles).
AIN had an opportunity to ride jumpseat with Hawker 800 pilots Jeff LaSalle and Julio Montalvo from their base in Lafayette, La., to Grand Junction, Colo. Their Hawker was due for routine maintenance at West Star Aviation, the company that installed the AutoPower system as well as the jet’s Aviation Partners winglets.
In the Hawker, not enough space is available near the throttle quadrant, so the autothrottle servo-motor clutch pack and pulley assembly is installed in the lower aft fuselage. The servo motor’s bi-directional sprag clutches allow the pilot to override the autothrottles, with no added force needed to move the power levers in any direction whenever necessary.
The installation includes an AutoPower computer, also mounted in the lower aft fuselage, an autothrottle system (ATS) control panel in the aft center console between the pilot seats and dual mode status display (MSD) indicators at the top of the instrument panel (one for each pilot). Autothrottles can be installed on airplanes with hydromechanical or Fadec engine controls, but in either case the Safe Flight system (unlike Airbus autothrottles) moves the power levers to match the power setting. Less hardware is needed in a Safe Flight Fadec autothrottle installation, and the hardware weight is about half that of a non-Fadec installation (less than 15 pounds compared with about 35 pounds). Installation cost in the Rockwell Collins Pro Line 21-equipped Hawkers is less than $200,000, according to Ken Bannon, Safe Flight director of commercial and corporate sales. West Star Aviation engineered the STC for the Hawker AutoPower system.
The advantages of autothrottles are subtle but clear once pilots have flown with the system. “Once you get used to autothrottles, you wouldn’t want to fly without them,” Bannon said. ATS works in every phase of flight, not just controlling thrust settings but also allowing pilots to set and maintain a desired speed in any configuration. This helps improve cruise efficiency and adds to passenger comfort. ATS also helps pilots avoid flying too slowly, automatically advancing the thrust if angle of attack increases to 0.6 or higher.
The safety benefit of holding a set speed can’t be over-emphasized. As LaSalle pointed out, the Hawker ATS makes it easy to set an airspeed when flying in a terminal area and not worry about adjusting power and checking the airspeed constantly while trying to follow vectors and look outside. During a circling approach, being able to set the speed and focus on looking for the runway is a big benefit of ATS. Add to that not worrying about flying too slowly, thanks to the 0.6 AOA limit, and the safety benefits are obvious.
Autothrottles in Action
We took off from Lafayette’s Runway 4R, with an initial climb to 6,000 feet. Before advancing the power levers, LaSalle pushed the go-around button to arm the ATS, and the MDS displayed “N1 to” in amber. LaSalle then pushed the thrust levers forward about two inches then activated the ATS engage button, which told the ATS to set takeoff power. The MSDs both displayed “N1 to” in green and the ATS servos moved the thrust levers to the takeoff power setting, then the engines’ digital controls managed the target thrust setting. After selection of climb mode by pushing the FLC button, the MSDs displayed “N1 clb” and the thrust levers moved back slightly.
The FMS performance page was already programmed with the desired speeds, including the 250-knot maximum below 10,000 feet and 270 knots for climb, which switched to Mach 0.7 as we climbed higher. At any time, the pilots could change the desired target speed by turning the flight guidance system speed knob.
We leveled off briefly at 6,000 feet and because the FMS was programmed with the 250-knot limit, the Hawker automatically maintained 250 knots while level. Pushing FLC to resume the climb mode resulted in more thrust-lever movement, then a speed increase (and more lever movement) to 270 knots once we passed 10,000 feet. It seems like a lot is going on, but the result of all this behind-the-scenes activity is that both pilots are able to focus more on flying and looking outside.
As we leveled off at FL340, the ATS held N1 at maximum thrust then moved the levers back to maintain the FMS programmed Mach speed of 0.75 (N1 of 94.6 percent). The MSDs switched to “speed” mode. The ATS held the Mach 0.75 speed for the rest of the cruise, although the pilots could easily change that by changing the target speed at any waypoint in the FMS. (Our maximum altitude was FL340 because this Hawker 800 was subject to an Airworthiness Directive related to its Aviation Partners winglets, limiting maximum altitude until the ailerons were rebalanced. The fix was done during the jet’s visit to West Star Aviation.)
For arrivals, LaSalle likes to set up the Star in the FMS, and the ATS will automatically hold required speeds, including during Vnav descents. LaSalle normally descends at Mach 0.76 or 300 knots. After setting an altitude below 10,000 feet, as the Hawker drops below 13,000 feet, the ATS automatically reduces power to bring the speed down to 250 knots at 10,000 feet. Once in the terminal area, LaSalle slows to 180 knots, and if he needs to slow down further momentarily, he can pull the thrust levers back, slow down, then release the levers and the ATS adds power to return to the 180 knots selected.
LaSalle demonstrated a go-around on final to Runway 11 at Grand Junction, pushing the go-around button on the thrust lever. The MSDs displayed “N1 ga” and the ATS ceased commanding the autothrottle servos while the engines’ digital controls maintained the target thrust. All LaSalle had to do was pull the nose up into the flight director v-bars, making his job of flying the airplane much easier.
The ATS can be set to maintain speed to the runway, then as the jet descends through 100 feet, the “speed” message on the MSDs starts flashing. At 50 feet, the message switches to “retard” (provided the flaps are set to 45 degrees and the radio altimeter output is valid) and the throttles automatically move to idle. LaSalle said he generally doesn’t use the ATS on visual approaches.
Installing the ATS in a Hawker 800 takes 10 to 12 days, according to West Star Aviation Hawker program manager Kendall Kreiling. The company has installed four systems so far, and to reduce cost owners generally schedule the job to coincide with other work that requires removal of the interior. There are approximately 500 Pro Line 21-equipped Hawkers that qualify for the ATS installation. “These airplanes are still valuable,” said Rodger Renaud, West Star’s COO.
For LaSalle’s flight operation, the safety aspects of the ATS aren’t the only reason he likes the system. “It was a combination of economy and safety,” he said, “safety being the number-one driver.” The combination of winglets and AutoPower delivers a range gain of about 200 nm, he reported. “On longer trips we’re seeing 8 to 10 percent less fuel burn than before. Now that I’ve had a year of operating the airplane with them, the ease and the workload that it takes off of us, it’s just tremendous.”
Safe Flight’s Bannon pointed out that for a Hawker 800 flown 640 hours a year, fuel savings range from nearly $20,000 to $50,000 a year, depending on average trip length. Another benefit, besides safety, comfort and efficiency, is that the Aircraft Bluebook adds $198,000 in value for Hawkers equipped with the AutoPower system.
