Why Some Jets Crash During Flight Testing

You may have read recently of a Bombardier Global 7000 flight-test aircraft making an emergency landing on 15 August when the right GE Passport engine experienced an in-flight flameout, according to an incident report issued by the National Transportation Safety Board (NTSB) of Canada. After reading this headline you are probably thinking this is a dangerous jet, as the engine failed.

This ultra-long-range business jet prototype was flying at 41,000ft when the incident occurred at 17:38 local time,156nm (290km) from the Bombardier flight-test centre at Wichita airport, Kansas.

The NTSB says the flameout was preceded by “high vibration and high inter-turbine temperature readings”. The pilots declared an emergency and carried out a single engine landing in Wichita, without further event, it says.

Bombardier is now reviewing the data “and troubleshooting the cause of the problem”, says the NTSB.

The three aircraft in the Global 7000 flight-test fleet have flown more than 500h, and Bombardier is now ramping up production of the $73 million business jet in preparation for its entry into service in mid-2018.

Launched in 2013, the 7,400nm (13,700km)-range Global 7000 is the largest and longest-range business jet in Bombardier’s seven-strong line-up.

The process of inflight testing is key before an aircraft can be certified to fly passengers. Part 23 airplanes generally have three years from the date of application to be certified; Part 25 airplanes have five years. This is a critical stage for any aircraft program because of something called “certification basis.”

When an aircraft manufacturer applies for a type certificate, the rules that are in force at the time of application are the rules with which the applicant must comply. If, for example, the FAA changed the certification rules after someone applied for certification, requiring that icing tests be done with 100-micron freezing drizzle instead of the current 40-micron droplet size, the applicant would not have to meet that new regulation.

The manufacturer will need 3 types of certificates issued.

1. Type Certificate,
2. Production Certificate
3. Airworthiness Certificate

The production certificate (PC) is almost as hard to obtain as the type certificate. The production certificate is basically a quality system that shows the FAA that a manufacturer is capable of reproducing many copies of an aircraft to the same standards.

Without the production certificate, FAA inspectors would have to inspect every aircraft coming off the assembly line before issuing the airworthiness certificate. With the PC in hand, the manufacturer’s designees can perform those inspections and sign off the airworthiness certificates.

The manufacturer has to consider how the airplane will be used, how pilots will train and the structure of continuous airworthiness (maintenance) programs. The sooner a manufacturer creates these programs, the better. Bombardier likes to have flight simulators ready before type certification and first delivery and even uses the simulators with their realistic aerodynamic modelling to help with aircraft development, according to chief airworthiness engineer Burns. 

As the certification program develops, the company simultaneously updates the simulator. “We use the simulator for engineering support for high-risk maneuvers and for workups,” he said. “It’s not so much practice but trying the maneuvers on the simulator before going in the actual aircraft.”

To speed certification outside Canada, because first deliveries typically take place in the U.S., Bombardier has asked regulators to work together closely. The Global Express program, for example, had three regulatory teams working in parallel on essentially the same certification program. For the Challenger 300, Bombardier’s latest clean-sheet design, there was one regulatory team led by Transport Canada with FAA and EASA (European aviation regulatory body) members, which helped make the 300 program much more efficient.

Certification by the FAA and EASA now takes place within weeks of Transport Canada’s OK,

Inevitably, there will be problems during certification, and sometimes they include big issues such as a redesign or change of materials. The FAA has the ability to generate issue papers. This is a good way to get the issue on the table, as they negotiate an agreement. This is used heavily in certification projects to resolve things that might come up that you didn’t know about in the pre-familiarization meeting.

In addition to evaluating certification compliance, FAA personnel will also pre-audit production facilities during this stage to help spot any problems that could hold up the program.

Before the aircraft manufacturer flies a prototype of the design, the FAA will need to issue an experimental type certificate. FAA personnel will conduct a safety review and check that the airplane conforms to its design. A plan for test flying will cover all requirements. And before FAA test pilots fly the airplane it must have flown through its full flight envelope. Flight testing is a challenging part of the certification program and can take a year or more, meeting requirements for compliance with various certification standards, noise testing, reliability testing, human factors analysis and qualitative assessments of the flying qualities to make sure it meets the standards for pilots to receive type ratings.

Proof-of-concept prototypes, which don’t conform to the final design, can be used for flight testing in areas where they do conform, if the test isn’t in an area where non-conformity is an issue.

Each aircraft type needs a production certificate. The best way to make the process of obtaining the production certificate smooth is to plan for production certification in parallel with type certification. That way, you don’t end up at the end of type certification with an airplane that isn’t ready for volume production because the FAA has to perform a detailed inspection on each airplane. The Production Certificate is like the aircraft’s birth certificate, allowing these aircraft to take the next stage of development.

Gulfstream are putting two new aircraft through this process right now, the G500 & G600. The four-aircraft strong G500 test fleet, along with the first production aircraft, have accumulated 2,900 flight hours over 745 flights over the past two years.

The G500 test fleet is now involved in functional and reliability testing, which is typically one of the last steps in the certification process. It involves flying a production-representative aircraft through a gauntlet of typical operational missions to prove to the FAA that the aircraft and on-board systems are reliable enough to enter service.

In a powerful demonstration of the G500's maturity, Gulfstream reprised Charles Lindbergh's historic transatlantic crossing on the 90th anniversary. Unlike Lindbergh's 33.5h flight, the G500 managed the crossing in a record-breaking 6h and 21min as a subsonic business jet, while cruising at Mach 0.90 at 45,000ft.

The G500 is the first Gulfstream aircraft – and the first in the business aviation segment – to feature fly-by-wire flight controls coupled to active control side-sticks, providing a new level of situational awareness in the cockpit along with flight envelope protections.

Gulfstream is using a slightly different flight testing program on the G500 after the 2011 G650 test flight crash. The NTSB blames the fatal accident on Gulfstream’s aggressive test flight schedule and failure to rectify pre-existing flaws in the ultra-long-range business jet’s takeoff speed.

According to investigators, the accident that killed four seasoned Gulfstream employees – which occurred after the jet’s wing struck the tarmac during a simulated engine-out takeoff – was technically the result of a stall and un-commanded roll during a simulated engine-out take-off.

As for deeper influential factors, however, the report points to a deadline-oriented company culture that, investigators say, placed performance before safety.

According to the NTSB, previous problems related to Gulfstream’s erroneously low take-off speed – including un-commanded roll events – occurred prior to the deadly crash in Roswell, New Mexico, but were not appropriately investigated by the company. NTSB officials also said Gulfstream team members involved in the flight testing program lacked clear roles and responsibilities, and that the company failed to enact the oversight necessary to ensure effective risk control.

The high-profile crash initially threatened to derail the G650 program, but Gulfstream later made up for lost time, receiving full certification.

Unfortunately sometimes test pilots die as they have to push these ‘new’ jets to the maximum to see how far they will go before they can be flown safely. As one test pilot I trained with a few years ago told me: “Test pilots are trained to fly the aircraft outside the envelope in order to define the safe barriers. Airline pilots are then trained to fly within the flight envelope to keep everyone safe.”

Some aircraft take just a few years to be certified, while others a lot longer. The Hondajet took over 10 years, as it was bringing to market a unique design and being the first jet produced by Honda they wanted to get it right.

Fabrizio Poli is an independant aviation consultant specialized in aircraft sales. He is also an accomplished Airline Transport Pilot having flown both private Jets and for the airlines. Fabrizio is also a bestselling author and inspirational speaker & has been featured on Russia Today (RT), TRT World, Social Media Examiner, Bloomberg, Channel 5, Chicago Tribune, Daily Telegraph, City Wealth Magazine, Billionaire.com, Wealth X, Financial Times, El Financiero and many other Media offering insight on the aviation world. Fabrizio is also regularly featured as an Aviation Analyst on Russia Today (RT) and TRT World. Fabrizio is also aviation special correspondent for luxury magazine, Most Fabullous Magazine. Fabrizio is also considered one of the world's top 30 experts in using Linkedin for business. You can tune in weekly to Fabrizio's business Podcast Living Outside the Cube available both in video & audio. You can also follow Fabrizio's aviation videos on Biz Jet TV . Fabrizio's latest book "Health4Flyers", the first natural-health book for pilots, flights attendants and frequent flyers is now available worldwide.