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T-45 Goshawk - Deficiencies

On 15 April 2017, the US Navy decided to put pilots and trainees back into the air, even though a firm solution has not been found. The $17 million aircraft will have teachers and students wear "modified" masks while researchers look into how to solve the oxygen issue. About 200 T-45C training jets were grounded in the first week of April after instructors protested unsafe flying conditions. Instructors will fly planes lower than 10,000 feet to avert using the jets’ oxygen systems, which had been causing pilots to undergo forced oxygen deprivation episodes in the air. Pilot trainees should be able to conduct about 75 percent of mission trainings as engineers and NASA scientists seek to determine the root cause for the problem.

Hypoxia, or lack of oxygen reaching the body's tissues, has plagued the service’s fleet of T-45s for years now. The on-board oxygen generation system that has given the T-45s woes previously was a thorn in the side of the F/A-18.

Conversion of the Hawk land-based aircraft to a naval trainer with carrier capabilities involved considerable research and development. In addition to the necessary strengthening of landing gear components and the inclusion of arresting gear, development work was required in numerous areas that were critical for carrier-based operations. Some areas of concern included the handling qualities, engine response characteristics, and stall characteristics of the T-45.

Cost, schedule, and performance risks were significant for the T-45 program. Foremost among the risk elements in the acquisition strategy was concurrency, a large overlap in aircraft development and production. The Navy did not schedule flight testing before the first production commitment, or schedule initial operational test and evaluation to be completed until after commitments had been made for 20 percent (60 aircraft) of the planned procurement.

The Navy and OSD instituted risk-reduction measures such as slowing production but have continued concurrent development and production. n 1988, following extensive preliminary flight-test evaluations by the Navy at the Patuxent River Naval Air Station in Maryland, the Navy cited several major deficiencies in the T-45. The deficiencies included high approach speed, slow engine thrust response, and longitudinal and lateral stability deficiencies. McDonnell Douglas and British Aerospace developed candidate solutions and recommended approaches to resolve these issues.

The stall characteristics of the initial T-45 configuration were judged to be unacceptable by the Navy on the basis of a severe wing-drop behavior at the stall and high approach speeds (aggravated by the increased weight required to strengthen the airframe for carrier operations). During the Navy's flight evaluations, the wing drop was so severe that uncommanded roll motions often exceeded 90 deg. The T-45 Program subsequently adopted a wing redesign, which incorporated wing leading-edge slats. The slats virtually eliminated the wing-drop tendency and lowered the carrier-approach speed to a more acceptable value.

Flight-test experience with the British Hawk aircraft indicated that the aircraft was very reluctant to spin and that attempts to intentionally spin the aircraft usually resulted in a spiral with rapidly increasing airspeed. Flight tests of the T-45 subsequently verified that during spin attempts, airspeed rapidly increased, and stabilized spins could not be obtained. As a result of this spin resistant behavior, the T-45 was not used for spin training (The T-2 and TA-4 had been used for spin training).

Inlet Performance Flight-test experience with the T-45 demonstrated that the aircraft sometimes experienced undesirable propulsion system characteristics during certain maneuvers. In particular, the aircraft engine experienced self-clearing "pop" stalls, pop surges, and occasional locked-in surges during simulated air-combat maneuvers and recovery maneuvers from aircraft (wing) stalls.

After initial testing revealed the aircraft’s design problems, the Office of the Secretary of Defense (0SD) withheld fiscal year 1989 funds that had been appropriated for aircraft. The Navy also canceled its funding request for procurement of 24 additional aircraft in fiscal year 1990. Operational test authorities in OSD and the Navy concluded that correction of the design flaws should be verified through testing before further production was authorized. Before the corrections were made, however, OSD released the fiscal year 1989 funds for the second production lot. The Navy requested $306 million to procure a third lot of 12 aircraft, 5 simulators, and associated equipment in fiscal year 1991.

By 1990 the T-45 Training System program faced significant cost, schedule, and performance risks. Although the system had been in production for over 2 years, a stable aircraft design had not yet been demonstrated in operational testing. Important cost and schedule issues also remain unresolved. The Congress declined to appropriate requested fiscal year 1991 funding for procurement of another lot of production aircraft.

The three major deficiencies of concern to aircrew that remained from the T-45 Full Scale Development (FSD) days ('89-'94) were probably ground handling, engine surge, and environmental control system fogging and icing. Blown tires on the catapult came to light once the aircraft began flying students operationally in '94. Not surprisingly, these fall into the number one, two, three and eight most desired items to be fixed from the Operator's Advisory Group (OAG) '99 list.

The aircraft design makes use of "off the shelf" hardware as much as possible and was found to have unusual directional control issues during ground operations. The aircraft was involved in numerous pilot-induced-oscillation incidents as well as observed to have unusual directional control reactions to failed main gear tires, a condition that is normally handled relatively easily by conventional aircraft steering control techniques. The behavior of the aircraft's tires had previously been modeled in simulators as a result of approximations provided in 40-year-old reference publications.

T-45 students suffered at least 16 incidents of blown tires on the catapult that have ultimately resulted in two Class A mishaps, including one fatality. Preceding an August '98 mishap, TRACOM experienced a blown tire incident roughly once every other Carrier Qualification (CQ) detachment. The T-45 project office tested a toe-bar modification (a small metal bar across the rudder pedal used as a proper position toe guide) in September 1998, which had been partially responsible for significantly reducing the incidents of blown tires on the catapult. Since the toe-bar modification was installed, the T-45 experienced one more blown tire incident on the catapult. The toe-bar modification was helpful in reducing the incidents of blown tires, but due to its ergonomic shortcomings, is certainly not the long term solution.

The T-45 was plagued with poor ground handling characteristics since its inception. Five of the ten Goshawk Class-A mishaps occurred during ground handling operations. While all of the mishaps had other complicating factors, the basic ground handling characteristics are the underlying cause that make incidents such as blown tires into a major emergency, vice the minor emergency it would be in any tactical fleet aircraft. Under normal, benign landing conditions the aircraft has a tendency to cause Pilot Induced Oscillations (PIO) on landing rollout, particularly when the jet is light. Numerous factors, identified by a joint Navy-McDonnell Douglas team formed in 1994, contribute to the undesirable characteristics.

The T-45 fleet experienced a growing looseness or freeplay in the stabilator due to wear in the various linkages of the longitudinal flight control system. The stabilator is free to rotate as much as 0.25o independent of commands from the pilot's longitudinal stick input. Engineers predict that with sufficiently large freeplay, the stabilator will encounter destructive flutter at high dynamic pressures within the NATOPS envelope. NAVAIR flutter engineers have however, through analysis, cleared the T-45 to fly the entire NATOPS envelope up to 0.25o of freeplay and to the limits of 350 KIAS, 0.7 IMN and 4 g's up to 0.30o freeplay. For freeplay values greater than 0.30o, the jet is not cleared to fly.

An excessive amount of water entered the Goshawk cockpit through the ECS system in the forms of liquid, fog, snow and ice. Ice chunks frequently navigate the defog ducts and impact the pilot's visor. Water also falls from the eye vents onto the consoles, potentially promoting corrosion. A multiphase program to identify the cause(s) and develop solutions began in the fall of 98. Phase I testing discovered that a pressure relief valve opened unexpectedly following a pressure build up in the water separator and coalescer sock. This phenomenon was associated with throttle transients or ECS controller changes, which resulted in a mild burst of airflow, ice and fog through the eye-vents/defog ducts, but the cause of the pressure build up was not understood. Additionally, temperature and flow oscillations were observed that appeared unrelated to any pilot activity. Phase II ground testing (June '99) identified a low frequency rumble in the ECS system that had not been seen previously. Some of the proposed solutions include; modified temperature selector to permit more precise control of the temperature, a coalescer ice screen to prevent ice from forming in the coalescer, and a modified vent demist valve to reduce the moisture in the system. These and other potential modifications will produce a long-term solution to ECS fog and ice in the T-45.

The NGS (Navigation Guidance System) the Standard Heading Attitude Reference System (SAHRS) used in the T-45A as the primary attitude source had an unacceptably high failure rate, and the vendor has ceased support for it. BAE/Marconi has developed NGS as a form, fit and function replacement.

In 1997 the project office conducted extensive tests with the baseline engine and a modified higher-bypass engine to see if the bypass ratio would improve the engine stall margin. The result was that the bypass did not improve the engine stall resistance sufficiently to go forward with production. PMA-273 continued the effort to reduce the engine's susceptibility to surges an 18 month flight test program, beginning fall 2000 that initially modified the way the Fuel Control Unit (FCU) schedules fuel to the engine, then follows up with tests of a modified engine inlet. T-45 test pilots and engineers evaluated the modifications for their efficacy at reducing engine surges and their effect on general engine handling qualities.

Based on data from the Navy, in 2016 the rate of physiological events (instances where a pilot experiences a loss in performance related to insufficient oxygen, depressurization or other factors present during flight) involving the life support system on the T-45 exceeded the rate for such events in the Navy’s F-18E/F fleet, which is itself was already unacceptably high. The T-45 is a training aircraft operated by student pilots who do not have extensive experience dealing with aircraft problems in flight. As a result, malfunctions in this aircraft may pose a heightened risk to both the aircraft crew and people on the ground in areas near training bases.

More than 100 instructors of the US Navy announced a boycott due to the fact that the management did not solve problems with the oxygen supply system on the carrier-based T-45 Goshawk training aircraft. On 07 April 2017, as many as 94 flights were cancelled between Naval Air Stations Kingsville, Meridian and Pensacola due to operational risk management (ORM) concerns raised by T-45C instructor pilots. Their concerns are over recent physiological episodes experienced in the cockpit that were caused by contamination of the aircraft's Onboard Oxygen Generation System (OBOGS). Chief of Naval Air Training (CNATRA) immediately requested the engineering experts at NAVAIR conduct in-person briefs with the pilots.

As a result, the US Navy halted flights. However, at first it was planned that only suspend flights for three days. It is reported that due to a problem with the oxygen supply, crew can experience histotoxic hypoxia - one of the oxygen deficiency types which leads to disorientation. The pilots said they did not feel safe. It was also reported that one of the hundreds of student pilots who raised the protest, is the son of US Vice President Mike Pence, passing flight training.

In an exclusive report from Fox News, the instructors say that the Navy's top leadership is not adequately addressing the problem, so they have stopped flying the T-45. One instructor told Fox News in an interview, "The pilots don't feel safe flying this aircraft." The representative of the United States Navy Cmdr. Jeannie Groeneveld said "We take seriously the concerns of our flight and entered a pause for T-45, to allow time for the leadership of naval aviation to communicate with pilots, to hear their concerns, and discuss the possibility of reducing the risks and the efforts that are being made now to fix this problem".

Vice Adm. Mike Shoemaker, Commander, Naval Air Forces, stated 09 April 2017 : "I continue to be impressed by the young men and women in Naval Aviation. Over the last two days, I have visited and talked extensively with the instructor pilots, students and staffs from our T-45C Training Wings at Naval Air Station (NAS) Meridian, NAS Kingsville and NAS Pensacola. They raised concerns about safety and the risks associated with physiological episodes (PEs) being caused by the oxygen breathing system in the T-45C. ... After frank discussions with the aircrew, leadership staffs and engineers, I will extend the operational pause for at least a week to allow time for our engineers to do a deeper dive into T-45 systems and for leadership to determine additional mitigation measures that will reduce the risks associated with the T-45 oxygen breathing system."

Vice Admiral Paul Grosklags explained to the House Armed Services Committee 07 May 2017 that two tactics had been deployed to deal with the jets' problem of oxygen shortages mid-flight. The Marines' and Navy's short-term plan was to equip T-45 Goshawks with "alerting and protective measures" to ensure pilots can continue their training programs on schedule, the commander said. Secondly, they will try to pin down the exact issue with the On-Board Oxygen Generation Systems (OBOGS).

Finding and addressing the root of the problem has proven difficult. Insufficient oxygen supply aboard the planes "as plagued the service's fleet of T-45s for years now. A top Navy official said the service had taken an "unconstrained resources" approach to fixing the jets, but even that hasn't worked. Mechanics from Boeing and the OBOGS manufacturer had been hard at work on fixing the issue. They also had the expertise of NASA engineers and scientists to contribute to their efforts.

What mystified military personnel is that OBOGS has been used on their Harrier jets without issue. Lt. Gen. Jon Davis remarked in wonder, "It's the same box in the Harrier. It's the same OBOGS box and we don't have a problem in Harriers. So what's different? What is different in the T-45s?" Even more confusing for military leaders is that negative physiological responses are on the rise in the Navy's fleet of Boeing F/A-18 Super Hornets, as well as in their EA-18 Growlers, too. "The system has worked for 20-plus years," Davis noted. "Something happened." Meanwhile, on 09 May 2017, a 55-plane strong fleet of fifth-generation F-35 combat aircraft was grounded after five pilots endured oxygen deprivation incidents.

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Page last modified: 11-06-2017 18:48:22 ZULU