A 737-10 airplane at maximum takeoff weight with worn-out brakes raced down a California runway last month at more than 200 miles per hour. The challenge for the Boeing test pilots: Bring the newest and largest 737 MAX model to a safe stop by only applying the brakes and not using the thrust reversers.
“The worn brakes are actually a requirement to show the worst possible scenario,” explained Capt. Kevin Zeznick, who was at the controls for the 737-10’s maximum brake energy (MBE) test, a critical certification milestone.
“We load the airplane up as heavy as it can go and go as fast as it would typically go on any takeoff and show that the airplane can stop and remain safe,” Zeznick said.
Take three minutes and watch: Boeing pilots conduct 737-10 maximum brake energy certification tests. (Wen Huber video © Boeing)
Demonstrating MAX performance
While the test is named after the airplane’s braking capabilities, it is equally important in validating the jet’s takeoff performance.
“For each takeoff, we have to look at what our brake performance is so we know the airplane can stop even if something goes wrong during the takeoff,” said Colston Polly, a certification engineer on the 737-10 program.
“So, whatever we do now, whatever performance we can get could be more benefit to our customers, like being able to be carry more passengers or fly more cargo,” Polly said.
The new 737-10, with a longer fuselage than the 737-9, can carry 10 more passengers for up to 230. The added capacity comes with only a minimal increase in operating costs, which means airlines flying the 737-10 can achieve the best per-seat economics of any single-aisle airplane.
Firefighters and Boeing engineers tend to a 737-10 flight test airplane after it completes a maximum brake energy testing in California. (Photo: Paul Weatherman © Boeing)
Showing off the new brakes
To accommodate the longer fuselage and handle the additional takeoff weight, Boeing engineers modified the 737 MAX landing gear and strengthened the brakes.
“This is certainly the highest-performing brake we’ve ever put on a 737,” said design engineer Evan Preston. “We added a fifth rotor to the brakes and a longer torque tube to get greater brake force and better stopping performance.”
A fully-loaded 737-10 test airplane accelerates down the runway at more than 200 miles per hour before attempting to abort takeoff as part of a maximum brake energy test. (Photo: Scott Dworkin © Boeing)
Performing the ultimate test
The Boeing Test & Evaluation team has been progressively testing the enhanced brakes, evaluating their performance while taking off and landing at slower, then higher speeds, on dry and wet runways, and with lighter and heavier weights.
In the ultimate test, the team loaded a 737-10 to its maximum takeoff weight of 197,900 pounds (89,765 kg) and machined the brakes down to within two percent of their wear life.
“At that point, we'll start the engines,” said Zeznick before the test. “And we have a requirement to complete a three-mile taxi and that is to simulate an aircraft leaving the gate and taxiing to a runway.”
Zeznick accelerated the airplane down the runway at Edwards Air Force Base north of Los Angeles, reaching 180 knots (207 miles or 333 kilometers per hour) before cutting back the throttles and fully applying the brakes.
The test airplane’s brakes are worn down to within two percent of their wear life and pilots must bring the plane to a stop without the use of thrust reversers. (Photo: Scott Dworkin © Boeing)
Watching and waiting
On the ground are observers and test conductors such as Flight Test Engineer Lauren Auerbach.
“We all chase the airplane on the runway as it's executing the rejected takeoff, so that we can all be in position as soon as possible. We are the test crew eyes that can really see what's going on,” said Auerbach.
Zeznick brought the airplane to a stop at about 11,000 feet on the 15,000-foot runway. At that point, everyone stopped and waited for the required five minutes, which represents the time for a rescue team at a commercial airport to reach the airplane.
In those five minutes, the energy from the rejected takeoff turned into extreme heat inside the brakes with temperatures exceeding 2,500 degrees Fahrenheit.
To address the heat, engineers designed the wheels with multiple thermal fuse plugs.
The significant braking force that is applied to the wheels translates to extreme heat exceeding 2,500 degrees Fahrenheit (1,371 degrees Celsius). (Photo: Alex Aristei © Boeing)
As designed, the plugs melted, releasing pressure from the tires. All four brakes survived the maximum energy for the required five minutes before fire crews moved in to douse the heat.
“The brakes performed as designed,” said Auerbach. “We got the expected brake pressure and the maximum brake energy, and the anti-skid [function] performed as expected.”
Zeznick added, “The acceleration and the stopping distances were very close to predictions. So, the airplane performed exceptionally well.”
Boeing engineers and test team members examine the wheel, brakes and tires after the pressure from the tires were safely released. (Photo: Evan Wollenberg © Boeing)
Doing it twice
With two brake suppliers on the 737 MAX, Boeing had to perform two MBE tests.
After each test, the ground crew must jack the airplane, remove the deflated wheel and tire assemblies, and change out the brakes so that the airplane can be tugged off the active runway. These activities extend a testing day that can stretch upwards of 12 hours, building on the months of test planning.
“The amount of coordination and cooperation amongst the teams is just astonishing,” said Zeznick.
In both MBE tests, the 737-10 brake system performed as Evan Preston and his engineering colleagues envisioned it.
“This better stopping performance that we’ve provided for the -10 along with all the other improvements on the -10 are going to provide flight manual performance that our airline customers are really going to love,” Preston said.
The 737 MAX Development team is conducting the remaining certification flight tests and completing the required documentation with the goal of certifying the 737-10 – and the smaller 737-7 – later this year.
The Boeing Test & Evaluation and 737 MAX Development teams successfully executed two maximum brake energy tests. In both tests, all four brakes survived the maximum energy for the required five minutes before fire crews moved in to douse the heat. (Photo: Scott Dworkin © Boeing)
For more information:
- Go inside the engineering design of the 737-10’s brakes, the highest-performing 737 brakes ever.
- Visit the Boeing Commercial Airplanes 737 MAX product page to learn more.