1 of 3 

Gulfstream Aerospace LP ¤ c/o IAI Dept. 4199 ¤ Ben Gurion Int'l Airport 70100 ¤ ISRAEL 

Tel: +972-3-935-6624 ¤ Fax: +972-3-935-6750 

July 30, 2015 GALP Ref: FAA/15220/CG 

Mr. Thomas Rodriguez 

Program Manager, International Branch, ANM-116 

Federal Aviation Administration 

Transport Airplane Directorate 

Aircraft Certification 

Subject: Request for Extension on FAA Exemption No. 10408 for Gulfstream G280 

Attachments: 

(A) Petition for partial Exemption Gulfstream Aerospace LP Uncontrollable High Thrust 

Failure Conditions Gulfstream Model G250 

(B) Exemption No. 10408 - Regulatory Docket No.FAA-2011-0686 

Dear Mr. Rodriguez, 

I am writing on behalf of Gulfstream Aerospace Limited Partnership (GALP), the holder of 

FAA type certificate A61NM for the Gulfstream G280 aircraft model, to request an extension 

of the current 19 December, 2015 deadline for obtaining FAA approval of an amended type 

design incorporating thrust-malfunction accommodation logic and for incorporating the 

design change on new production aircraft. GALP hereby respectfully requests an extension 

of twelve (12) months from the current deadline based upon the justifications provided 

herein. 

On December 19, 2011 the Federal Aviation Administration (FAA) granted exemption 10408 

(petition and grant attached) associated with 25.901(c) of Title 14 of the Code of Federal 

Regulations and the Uncontrollable High Thrust (UHT) scenario. More than eight months 

later, on 30 August 2012, the FAA issued type certificate A61NM for the Gulfstream G280. 

The technical basis and merits for granting this exemption for the G280 are well documented 

in attachments (A) and (B) and remain equally compelling at this time. 

We have been working intensively and very closely with the G280 engine manufacturer, 

Honeywell, in developing the amended type design intended to address the UHT issue. The 

software which provides the required UHT protection resides in the engines Full Authority 

Digital Engine Control (FADEC). The FADEC software version 2.0 has been in development 

now for several years to support the requirements of this exemption as well as to incorporate 

various improvements. Following the review of recent flight test data and performance 

calculations we have identified additional issues requiring correction by Honeywell. 
 

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Honeywell estimates that incorporation and certification of the necessary corrections will 

require an additional four months, beyond the eight months discussed above. The result 

being a total requested extension of twelve (12) months to December 2016. 

A review of several FAA exemptions related to the UHT issue and compliance with 25.901(c) 

with a focus on the issue dates of the exemption and of the type certificate clearly show that 

in the case of the G280 the more than eight (8) month span between the exemption and type 

certificate issue dates is extreme. Issuing the exemption so far in advance of the issuance 

of the type certificate, and attaching the four year compliance requirement to the exemption 

issuance date rather than the type certificate issuance date in effect started the “timer” for 

providing a new design (amended type design) while we were still developing / certifying the 

initial type design. To illustrate this we provide below a summary of a number business 

aviation aircraft models receiving type certification in the same period. This is by no means 

an all inclusive list but illustrates the issue quite clearly. 

TC Holder Aircraft Model TC No. TC Issue

Date

Exemption

Issue Date

FAA

Exemption

No.

Gulfstream Aerospace

LP

G280 A61NM 8/30/2012 12/19/2011 10408

Bombardier Challenger 350

(BD‐100‐1A10)

T00005NY 6/24/2014 6/24/2014 11013

Gulfstream Aerospace

Corporation (GAC)

Gulfstream GVI

(G650)

T00015AT 9/7/2012 8/28/2012 10614

Cessna Model 680

Sovereign+

T00012WI 12/20/2013 11/29/2013 10902

The additional four months requested, beyond the eight months justified due to the 

significant difference between exemption and type certificate issue dates, poses no adverse 

effect on safety of the aircraft, its operators or to the public in general. The case for granting 

this exemption made in the original GALP petition (Attachment (A)) would not be impacted 

by this extension. In order to place this in the correct perspective it is important to point out 

that at the G280 production rate established for the period covering the additional four 

months requested only an additional 6-7 aircraft would be entering into service under the 

exemption if the full twelve month extension is granted by the FAA. 

In addition to the inherent limited exposure and extremely low occurrence rate of such 

events throughout the industry, the FAA required that the G280 Aircraft Maintenance Manual 

(AMM) contain mandatory reporting requirements for engine controls related Line 

Replaceable Units (LRU) and their specific failure modes which could lead to a UHT event. 

While the reporting requirement is from the operator to the FAA, we have no records of any 

such reports having been made. 
 

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GALP respectfully requests that the FAA not delay taking a decision on this request by 

foregoing the publication and public comment procedures. GALP feels this request is 

supported by the position that granting of this extension has no impact upon public safety 

nor does it represent a matter of compelling interest to the public. Additionally, a delay in 

acting on this request for extension caused by publication could have an adverse effect on 

GALP and the operators of the G280 airplanes who have made substantial commitments 

associated with aircraft deliveries. 

We greatly appreciate the FAA’s consideration to this request and look forward to its timely 

processing. 

Regards, 

Charly Gaber 

Airworthiness & Certification Manager 

Gulfstream Aerospace LP 

P.O. Box 1036 

Airport City 

7019900, Israel 

e-mail: Charly.Gaber@gulfstream.com 

Telephone: +972-3-935-6627 

Fax: +972-3-935-6750 

cc: D. Lawton, J. Gibbs, D. Such, S. Cottrell, I. Kalal, M. Kollet, T. Nir 

 M. Fagan, File 
 

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Petition for partial Exemption

Gulfstream Aerospace LP

Uncontrollable High Thrust Failure Conditions

Gulfstream Model G250

Relief from section 14 CFR Part 25.901(c)

 Section 25.901(c) requires in part that “no single failure or malfunction or probable combination of 

failures will jeopardize the safe operation of the airplane”. 

Gulfstream Aerospace LP respectfully requests a time limited partial exemption to Federal 

Aviation Regulation (FAR) Part 25.901(c) of Title 14, CFR, for certain extremely remote 

powerplant failures that could affect only a very limited portion of the flight envelope of the 

Gulfstream Model G250. 

This partial exemption requires Gulfstream Aerospace LP to demonstrate that the overall 

level of safety of the thrust control system of G250 model will not be less than that of the 

current transport category aircraft fleet. For this purpose, Gulfstream Aerospace LP 

analyzed the Uncontrollable High Engine Thrust failure rate data of the Honeywell AS907 

engine family and performed engineering-simulated flights per scenarios specified in CAAI 

/ FAA Issue Paper P-10. 

The exemption is required for a period of 4 years after FAA validation. During this period, 

GALP and Honeywell will develop and make available improved UHT logic which will 

mitigate the effects of an UHT event in some scenarios. The improvement will be certified 

as a product improvement prior to the expiration of the time frame specified above and will 

be implemented in all new production a/c manufactured after this date. It is not the 

intention of GALP to retrofit previously fielded aircraft (estimated 100 a/c) with the 

improved UHT logic. 

The nature of this petition for partial exemption is similar to previously granted exemptions 

for the Airbus models A340-500, A340-600, the Embraer models EMB-135BJ, EMB145XR, the Boeing model 757-300 and 777’s and the Gulfstream Models G150, G-1159, 

G-IV, GV and GV-SP. 

 Supportive Information: 

A committee consisting of representatives from the FAA, the JAA, airplane manufacturers, 

and engine manufacturers was formed in 1998 to study strategies for providing additional 

protection from thrust control malfunctions resulting in un-commanded high thrust. The 

committee found that for the existing in-service airplanes, whose propulsion systems have 

demonstrated a level of reliability on the order of one un-commanded high thrust event per 

10 million flight hours, it would not be in the public interest to mandate major and novel 

design changes in an attempt to eliminate the already small potential exposure to uncommanded high thrust malfunctions resulting from single failures. The committee’s 

recommended approach to ensure continued high levels of reliability for all presently 

certified models is to monitor in-service performance and, if any unacceptable failure 

modes are identified, to take prompt corrective action by introducing focused design 

improvements using proven technology. 
 

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Tel: +972-3-935-6624 ¤ Fax: +972-3-935-6750 

Full compliance with 14 CFR 25.901(c) would require introduction of complicated and 

novel design changes to the G250 Program, such as the Thrust Control Malfunction 

feature. It is recognized that experience with this feature over the past few years has 

demonstrated that such a feature can safely and reliably eliminate most of the causes of 

noncompliant UHT failures conditions. 

 At this time GALP is considering the right solution to incorporate this feature in the G250 

aircraft. 

 The petitioner intends to demonstrate that those combinations of failures that could 

jeopardize safe operation meet the intent of § 25.901(c) in that they are not “probable 

combinations1

.” Conversely, the petitioner does not always intend to demonstrate that 

those single failures which could jeopardize safe operation comply with § 25.901(c). 

Compliance with § 25.901(c) requires each identified single failure be assumed to occur 

under all anticipated combinations of airplane operating and environmental conditions. 

While the single failures themselves must be assumed to occur regardless of their 

probability2

, probability can be considered when determining what combinations of 

operating and environmental conditions are anticipated to occur in the fleet life of the 

airplane type. Single failures do not need to be assumed to occur under conditions that 

are in and of themselves not expected to occur. 

The engine control system for the G250 is a FADEC-based system and as such, future 

design changes to this control system should provide opportunities to significantly reduce 

or even eliminate the subject non-compliance. The conditions established by the FAA for 

granting this partial exemption, when applied to each proposed design change, are 

intended to take full advantage of each practicable opportunity for improvement while 

affording the petitioner all warranted flexibility to certificate non-compliant derivative 

designs.

 Issue of Public Interest

A control system that might eliminate all failure modes of concern for the Gulfstream 

Aerospace LP G250 Model (such as the Thrust Control Malfunction Unit), would require 

 1

 The term “probable,” as used in § 25.901(c) has a very different meaning than the same term as subsequently used in association with 

§ 25.1309(b) compliance. As used in §25.901(c), "probable" means “foreseeable”. In §25.1309(b) terms, this means the subject failure 

conditions are "anticipated to occur” (i.e. aren't "extremely improbable”). 

2

 While probability has been an acceptable means of supporting a finding that a particular "combination" of failures are not "probable", 

any single failure where the physics of the failure can be identified is typically "anticipated to occur" unless that occurrence within the 

relevant exposure can be clearly and acceptably ruled out, as is the case for those structural failures specifically excepted by the rule itself. 
 

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significant modifications to the current engine control system. A redesign of previously 

approved engine control system architecture would impact the schedule of the Gulfstream 

Aerospace LP G250 Model program. 

Since this feature is still in development, requiring the G250 Model to fully comply with this 

rule would prevent Gulfstream Aerospace LP from certifying the aircraft on a timely and 

competitive schedule, putting it in an unfair disadvantage to its competitors in Europe and 

with other foreign aircraft manufacturers. This could result in economic disadvantage to 

the company, its employees and communities who are dependent upon this commerce. 

Additionally, Gulfstream Aerospace LP is a highly reputable supplier of transport aircraft 

that serve vital commercial and governmental entities throughout the world. These 

operators depend on the improved technology in new Gulfstream Aerospace LP models to 

effectively and safely meet the needs of national and international commerce, governance 

and charitable missions throughout the world. 

 Effect of the Exemption on Safety

As stated above, Gulfstream Aerospace LP will demonstrate that the risks due to 

uncontrollable high thrust failure conditions on G250 will not exceed those currently known 

and accepted for comparable existing transport category airplanes. This means that 

granting partial exemption should not adversely affect and, in fact, should improve the 

average per flight hour risk within the current transport airplane fleet. 

For those existing transport airplanes re-evaluated to date, the conditions under which an 

uncontrollable high thrust failure may jeopardize the safe operation of the airplane are 

limited to specific aborted takeoff scenarios. Given that these scenarios occur, there is still 

a low probability that any serious injury will develop. This limited exposure, in conjunction 

with the low probability of occurrence, means that an Uncontrolled High Thrust event is a 

relatively low per flight hour risk. This assessment is supported by the fact that the 1997 

Saudi Arabian Airlines Boeing 737-200 accident is the only one attributed to these types of 

failures and there were no serious injuries in that accident. 

It is the spectra of this low per-flight-hour risk accumulating indefinitely on many, if not 

most, existing and future transport airplanes that are the primary concern driving 

development of the FAA’s “Thrust Control Malfunction Airworthiness Program.” To date, 

corrective actions under 14 CFR part 39 have only been deemed warranted when the 

uncorrected risks for a particular type design were considered significantly greater than 

those required by the conditions and limitations of this petition for partial exemption. 

Gulfstream Aerosapce LP agrees to demonstrate that all practicable actions have been 

taken to minimize the adverse effect on safety associated with granting of the exemption 

from 14CFR 25.901(c) for the G250 Model aircraft. 

Furthermore, Gulfstream Aerospace LP would like to emphasize the following: 
 

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 The G250 aft fuselage mounted engine design (i.e. relative close proximity to A/C 

centerline) mitigates much of the adverse yaw condition that may be generated during a 

single engine uncontrollable high thrust event on other designs. 

 The G250 incorporates a Thrust Compensator feature that compensates the thrust 

asymmetry by rudder movement. This feature is automatically actuated when thrust 

asymmetry occurs and it augments the aircraft controllability when UHT is encountered 

(as demonstrated in the engineering simulation). 

 The controllability assessment during Uncontrolled High Thrust was evaluated by 

conservative Engineering simulations and will be verified in a full Level D airplane 

simulator as soon as it is available. 

 It was found that the G250 Model complies with 14CFR 25.901(c) for any foreseeable 

uncontrollable high thrust failure conditions, except for very limited window(refer to 

Flight Simulator test report, doc number: 30P011/071452) : 

 RTO scenarios where the malfunction occurs below 50kts, as was demonstrated in 

simulation flights. This scenario is included in the request for exemption since 

the Nose Wheel Steering, which is essential for controlling the A/C on ground at 

low speeds was not available on the simulator. 

 The frequency of occurrence of uncontrollable high thrust failure condition on the G250 

was calculated to be ~2 E-8 which is less than the known average industry value of 

one per ten million airplane operating hours. 

 Thrust Control Malfunction unit is in development and will be incorporated in the G250. 

Gulfstream Aerospace LP has verified that the G250 Model exposures and failure rates 

are such that this airplane should not exceed the known average per flight-hour risks of 

comparable existing transport airplanes. Making this statement a condition of this 

exemption, in combination with the condition to minimize that risk, means that granting this 

exemption should not adversely affect and in fact, should improve the average per flight 

hour risk within the current transport airplane fleet. 

In support of this exemption and prior to customer delivery of any G250 aircraft, 

Gulfstream Aerospace LP will develop and obtain CAAI / FAA acceptance of the 

instructions for continued airworthiness. Further, the Uncontrollable High Engine Thrust 

failures shall be considered mandatory reportable to the CAAI/FAA under 14 CFR Part 

21.3, for any airplane certificated under this exemption. 

The limited exposure, in conjunction with the historically low occurrence rates throughout 

the industry, makes this a relatively low per flight hour risk. This assessment is further 

supported by the fact that the 1997 Saudi Arabian Airlines Boeing 737-200 accident is the 

only event attributed to these types of failures and there were no serious injuries in that 

accident. 
 

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 Waiver of Notice and Public Procedure

Gulfstream Aerospace LP respectfully requests that, and believes that good cause exists 

why, action on this petition should not be delayed by publication and comment procedures. 

Gulfstream Aerospace LP feels this request is supported by the following reasons: 

1. The petitioner’s request does not set a precedent because the relief requested herein 

is identical to exemptions granted previously. 

2. A delay in acting on the petition caused by publication could have an adverse effect on 

Gulfstream Aerospace LP and the operators of the G250 airplanes who have made 

substantial commitments and plans for the introduction of the airplanes into the fleet to 

meet mission needs. 

 Conclusion

Gulfstream Aerospace LP believes that the above arguments favor a time limited 

exemption from 14 CFR 25.901(c) for the aft fuselage mounted installation of the 

Honeywell FADEC controlled engines onto the GULFSTREAM AEROSPACE LP G250 

aircraft. Additionally, Gulfstream Aerospace LP believes that any risks due to an 

Uncontrollable High Thrust failure condition on G250 will not exceed those currently known 

and accepted for comparable existing transport category airplanes and that an exemption 

is in the public interest. Gulfstream Aerospace LP requests that the privileges of this 

exemption would apply outside the United States due to the transoceanic capability of the 

G250 aircraft and the character of mission for many of our operators. 
 

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 APPENDIX A 

 ENGINE CONTROL SYSTEM OVERVIEW. 

 The G250 is equipped with two Honeywell AS907-2 turbofan engines of 4.2 to 1 bypass ratio, enclosed by nacelles 

and mounted to pylons extending laterally outward from the aft fuselage section. 

 A throttle control assembly (TQA) is installed in the flight compartment with all controls on the pedestal accessible 

to both pilot and copilot. The engine thrust is controlled by the pilot with the throttle lever by means of Full Authority 

Digital Electronic Control (FADEC) which is electrically monitoring the thrust lever position (thrust by wire). Each of 

the engine power controls consist of a throttle lever, thrust reverser lever, AT (Autothrottle) Engage/Disengage switch, 

AT Quick Disconnect switch, and Takeoff/Go- Around switch. A single APR switch is located forward of the TQA. If 

the APR switch is selected, an engine will engage APR mode if the respective throttle lever is moved into the takeoff 

range. A RUN/STOP switch is provided to shutdown each engine. 

 G250 Engine control system –

 Uncontrolled engine overspeed safety features.

1. N2 Overspeed Shutdown 

 The N2 overspeed system protects against overspeed of both rotor systems (N1 and N2) driven 

by control system failures. These failures may include software errors and electrical malfunctions 

of the FADEC or HMU mechanical malfunctions that result in uncommanded acceleration or over 

fueling of the engine. The N2 overspeed protection system is implemented through dedicated 

circuits within the engine FADEC controller. These circuits operate independently of the CPU and 

software that control engine operation. 

 Each ECU contains two N2 overspeed detection circuits. One circuit monitors the PMA N2 signal, 

while the other monitors the gearbox mounted N2 monopole signal. When both circuits detect an 

overspeed condition (defined as N2>103 percent ±0.5 percent), the shutoff solenoid is energized. 

In addition, the run coil (used by software to enable fuel flow on start) is disabled by overspeed 

detection circuit and not the software. The shutdown coil is maintained energized and the run coil 

disabled until 35 percent speed, when the overspeed circuits unlatch. During the 

flameout/deceleration from overspeed to 35 percent, software attempts to de-power the run 

solenoid and igniters, also closing the main MV to positively latch the shutdown. Either engine 

FADEC controller can detect an overspeed condition and thus shut down the engine, even if that 

channel is not the controlling channel. The N2 overspeed system is checked on each start and 

each shutdown.

2. Broken Low Pressure Shaft (N1) Overspeed Shutdown 

 The N1 broken shaft system provides protection against LPT overspeed driven by LPT shaft 

breakage. In order to obtain the rapid response needed for this function, the system is 

implemented through dedicated circuits within the ECU, and independent of the CPU. Note that N1 

overspeed protection is implemented via the N2 overspeed protection system. A power turbine 

position detector, mounted behind the final 

 LPT stage, senses LPT position and signals the N1 OSSO circuit, if LPT position shifts rearward 

enough to indicate a severed LPT shaft. The N1 OSSO circuit then initiates an engine shutdown 

using the same OSSOV as the N2 OSSO system. The power turbine position detector is a device 

that breaks an electrical link, or circuit, to indicate rearward motion of the LPT. Redundant wiring to 

the link ensures that open circuit failures of connectors or harnesses do not result in false broken 

shaft detection. Each engine FADEC contains two identical but independent N1 OSSO detection 

circuits that monitor the link. A broken shaft is detected when both N1 OSSO detection circuits 

simultaneously detect a broken link with continuity on all other detector lines continuously for 1.0 to 

1.5 milliseconds. When a broken shaft is detected, the circuit energizes the overspeed shutoff coil. 
 

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The circuitry simultaneously shorts out the run coil to remove this opposing force. FADEC ensures 

that the coil voltage collapses quickly to remove any opposing force. 

 Within a few hundred milliseconds of the detected event, software also initiates a normal 

shutdown, disabling ignition, deenergizing the run coil, and closing the MV latching in the 

shutdown. The event is stored in NVM, and software will not allow another engine start until proper 

maintenance action is taken. 

 The N1 broken shaft protection system is checked on each startup and shutdown. 
Exemption No. 10408 

UNITED STATES OF AMERICA 

DEPARTMENT OF TRANSPORTATION 

FEDERAL AVIATION ADMINISTRATION 

RENTON, WASHINGTON 98057-3356 

In the matter of the petition of 

Gulfstream Aerospace LP 

for an exemption from § 25.901(c) of Title 14, 

Code of Federal Regulations 

Regulatory Docket No.FAA-2011-0686 

GRANT OF EXEMPTION 

On June 21, 2011, Mr. Baruch Marom, Gulfstream Aerospace LP (GALP), P.O. Box 1036, 

Airport City 70100, Israel, petitioned for an exemption from the “no single failure” criteria of 

§ 25.901(c) of Title 14, Code of Federal Regulations (14 CFR) as it relates to certain extremely 

remote, uncontrollable, high-thrust failure conditions. Recent studies and service experience 

indicate that some existing transport-category airplanes do not strictly comply with § 25.901(c) 

for certain uncontrollable high-thrust failure conditions. The proposed exemption, if granted, 

would permit type certification of similarly non-compliant GALP Model G280 airplanes with 

Honeywell AS907 engines. 

The petitioner requires relief from the following regulations: 

Section 25.901(c) as amended by Amendments 25-1 through 25-84: 

(c) For each powerplant and auxiliary power unit installation, it must be established that 

no single failure or malfunction or probable combination of failures will jeopardize the 

safe operation of the airplane except that the failure of structural elements need not be 

considered if the probability of such failure is extremely remote. 

The petitioner supports its request with the following information: 

This section quotes the relevant information from the petitioner’s request. The complete petition 

is available at the Department of Transportation’s Federal Docket Management System, on the 

Internet at http://regulations.gov, in docket no. FAA-2011-0686. 
 2 

Gulfstream Aerospace LP respectfully requests a time limited partial exemption to 

Federal Aviation Regulation (FAR) Part 25.901(c) of Title 14, CFR, for certain extremely 

remote powerplant failures that could affect only a very limited portion of the flight 

envelope of the Gulfstream Model G280. 

This partial exemption requires Gulfstream Aerospace LP to demonstrate that the overall 

level of safety of the thrust control system of G280 model will not be less than that of the 

current transport category aircraft fleet. For this purpose, Gulfstream Aerospace LP 

analyzed the Uncontrollable High Engine Thrust failure rate data of the Honeywell 

AS907 engine family and performed engineering-simulated flights per scenarios 

specified in CAAI / FAA Issue Paper P-10. 

The exemption is required for a period of 4 years after FAA validation. During this 

period, GALP and Honeywell will develop and make available improved UHT logic 

which will mitigate the effects of an UHT event in some scenarios. The improvement will 

be certified as a product improvement prior to the expiration of the time frame specified 

above and will be implemented in all new production a/c manufactured after this date. It 

is not the intention of GALP to retrofit previously fielded aircraft (estimated 100 a/c) 

with the improved UHT logic. 

The nature of this petition for partial exemption is similar to previously granted 

exemptions for the Airbus models A340-500, A340-600, the Embraer models EMB135BJ, EMB145XR, the Boeing model 757-300 and 777’s and the Gulfstream Models 

G150, G-1159, G-IV, GV and GV-SP. 

Supportive Information: 

A committee consisting of representatives from the FAA, the JAA, airplane 

manufacturers, and engine manufacturers was formed in 1998 to study strategies for 

providing additional protection from thrust control malfunctions resulting in uncommanded high thrust. The committee found that for the existing in-service airplanes, 

whose propulsion systems have demonstrated a level of reliability on the order of one uncommanded high thrust event per 10 million flight hours, it would not be in the public 

interest to mandate major and novel design changes in an attempt to eliminate the already 

small potential exposure to uncommanded high thrust malfunctions resulting from single 

failures. The committee’s recommended approach to ensure continued high levels of 

reliability for all presently certified models is to monitor in-service performance and, if 

any unacceptable failure modes are identified, to take prompt corrective action by 

introducing focused design improvements using proven technology. 

Full compliance with 14 CFR 25.901(c) would require introduction of complicated and 

novel design changes to the G280 Program, such as the Thrust Control Malfunction 

feature. It is recognized that experience with this feature over the past few years has 

demonstrated that such a feature can safely and reliably eliminate most of the causes of 

noncompliant UHT failures conditions. 
 3 

At this time GALP is considering the right solution to incorporate this feature in the 

G280 aircraft. 

The petitioner intends to demonstrate that those combinations of failures that could 

jeopardize safe operation meet the intent of § 25.901(c) in that they are not “probable 

combinations.” Conversely, the petitioner does not always intend to demonstrate that 

those single failures which could jeopardize safe operation comply with § 25.901(c). 

The engine control system for the G280 is a FADEC-based system and as such, future 

design changes to this control system should provide opportunities to significantly reduce 

or even eliminate the subject non-compliance. The conditions established by the FAA for 

granting this partial exemption, when applied to each proposed design change, are 

intended to take full advantage of each practicable opportunity for improvement while 

affording the petitioner all warranted flexibility to certificate non-compliant derivative 

designs. 

Issue of Public Interest 

A control system that might eliminate all failure modes of concern for the Gulfstream 

Aerospace LP G280 Model (such as the Thrust Control Malfunction Unit), would require 

significant modifications to the current engine control system. A redesign of previously 

approved engine control system architecture would impact the schedule of the Gulfstream 

Aerospace LP G280 Model program. 

Since this feature is still in development, requiring the G280 Model to fully comply with 

this rule would prevent Gulfstream Aerospace LP from certifying the aircraft on a timely 

and competitive schedule, putting it in an unfair disadvantage to its competitors in 

Europe and with other foreign aircraft manufacturers. This could result in economic 

disadvantage to the company, its employees and communities who are dependent upon 

this commerce. Additionally, Gulfstream Aerospace LP is a highly reputable supplier of 

transport aircraft that serve vital commercial and governmental entities throughout the 

world. These operators depend on the improved technology in new Gulfstream 

Aerospace LP models to effectively and safely meet the needs of national and 

international commerce, governance and charitable missions throughout the world. 

Effect of the Exemption on Safety 

As stated above, Gulfstream Aerospace LP will demonstrate that the risks due to 

uncontrollable high thrust failure conditions on G280 will not exceed those currently 

known and accepted for comparable existing transport category airplanes. This means 

that granting partial exemption should not adversely affect and, in fact, should improve 

the average per flight hour risk within the current transport airplane fleet. 

Gulfstream Aerospace LP agrees to demonstrate that all practicable actions have been 

taken to minimize the adverse effect on safety associated with granting of the exemption 
 4 

from 14CFR 25.901(c) for the G280 Model aircraft. Furthermore, Gulfstream Aerospace 

LP would like to emphasize the following: 

 The G280 aft fuselage mounted engine design (i.e. relative close proximity to A/C 

centerline) mitigates much of the adverse yaw condition that may be generated 

during a single engine uncontrollable high thrust event on other designs. 

 The G280 incorporates a Thrust Compensator feature that compensates the thrust 

asymmetry by rudder movement. This feature is automatically actuated when 

thrust asymmetry occurs and it augments the aircraft controllability when UHT is 

encountered (as demonstrated in the engineering simulation). 

 The controllability assessment during Uncontrolled High Thrust was evaluated by 

conservative Engineering simulations and will be verified in a full Level D 

airplane simulator as soon as it is available. 

 It was found that the G280 Model complies with 14CFR 25.901(c) for any 

foreseeable uncontrollable high thrust failure conditions, except for very limited 

window(refer to Flight Simulator test report, doc number: 30P011/071452): 

 RTO scenarios where the malfunction occurs below 50kts, as was 

demonstrated in simulation flights. This scenario is included in the request 

for exemption since the Nose Wheel Steering, which is essential for 

controlling the A/C on ground at low speeds was not available on the 

simulator. 

 The frequency of occurrence of uncontrollable high thrust failure condition on the 

G280 was calculated to be ~2 E-8 which is less than the known average industry 

value of one per 10 million airplane operating hours. 

 Thrust Control Malfunction unit is in development and will be incorporated in the 

G280. 

Gulfstream Aerospace LP has verified that the G280 Model exposures and failure rates 

are such that this airplane should not exceed the known average per flight-hour risks of 

comparable existing transport airplanes. Making this statement a condition of this 

exemption, in combination with the condition to minimize that risk, means that granting 

this exemption should not adversely affect and in fact, should improve the average per 

flight hour risk within the current transport airplane fleet. 

In support of this exemption and prior to customer delivery of any G280 aircraft, 

Gulfstream Aerospace LP will develop and obtain CAAI / FAA acceptance of the 

instructions for continued airworthiness. Further, the Uncontrollable High Engine Thrust 

failures shall be considered mandatory reportable to the CAAI/FAA under 14 CFR Part 

21.3, for any airplane certificated under this exemption. 
 5 

Federal Register publication 

A summary of this petition was published in the Federal Register on July 29, 2011. The FAA 

received no comments. 

FAA Analysis: Introduction 

Granting this exemption requires the petitioner to show, as required by § 11.81(d), that the 

request is in the public interest, and, as required by § 11.81(e), that the exemption will not 

adversely affect safety, or that a level of safety will be provided that is equal to that provided by 

the rules from which the exemption is sought. 

FAA Analysis: Public Interest 

In their petition, Gulfstream Aerospace LP (GALP) acknowledges that the Model G280 type 

design currently proposed for certification will not fully comply with the “no single failure” 

provision of § 25.901(c) as it relates to certain uncontrollable high-thrust failure conditions. 

Following the investigation of a 1997 Saudi Arabian Airlines Boeing 737-200 accident, it was 

recognized that this type of non-compliance had long been endemic in the state-of-the-art 

engine-control architectures of most transport-category airplanes. Furthermore, it was going to 

be very challenging to develop and validate safe practical compliant alternatives to that 

architecture. Since that time, most type-certification programs have included some sort of 

exemption for uncontrollable high-thrust failure conditions. However, one of the conditions for 

granting each of those exemptions has been that the applicant take all practicable actions to 

minimize the adverse effects on safety associated with granting the exemption. 

In the process of evaluating the proposed GALP Model G280 type design, the FAA recognized 

that GALP had not taken all feasible actions to eliminate or further reduce the risks associated 

with this non-compliance. Specifically, thrust-malfunction-accommodation logic (i.e. logic that 

identifies and safely accommodates any sustained, substantial discrepancy between the actual 

and commanded thrust, as sensed and validated by the engine control) was not incorporated. 

Such thrust-malfunction-accommodation logic incorporated into some recently approved 

airplane type designs has proven itself to be practical and effective at eliminating most 

noncompliant, uncontrollable, high-thrust failures except for those associated with the airplane 

throttle system (e.g. stuck throttle, disagreement between actual throttle position and that input to 

the engine control, etc.). 

However, GALP did not become aware that thrust-malfunction-accommodation logic was 

considered a practical and effective mitigating action until it was too late to safely develop and 

validate such critical engine-control logic without substantially impacting their delivery 

schedule, which made incorporation of such engine-control logic, before certification, 

impractical. Consequently, GALP has requested this exemption to allow them up to 4 years from 

the date of granting to develop, certificate, put into production, and facilitate retrofit of 

acceptable thrust-malfunction-accommodation logic, eliminating all noncompliant, 
 6 

uncontrollable, high-thrust failures, except perhaps those due to failures within the airplane 

throttle system. 

If the FAA were to deny this petition, that would substantially delay delivery of these aircraft 

and put considerable schedule pressure on the development and certification of critical enginecontrol-logic changes. This would not only have the adverse economic and logistical impacts 

noted by the petitioner, but also inherently increase the risk of undiscovered development errors 

in the new thrust-malfunction-accomodation logic. The malfunctioning of this logic could have a 

more adverse impact on safety than would its absence; the FAA considers it critical to safety to 

allow ample time for proper development and validation of such logic systems. 

In consideration of the above, and with the finding below that granting this petition will not 

adversely affect safety, the FAA concludes that granting this time-limited exemption is in the 

public interest. 

FAA Analysis: Effect on Safety 

The petitioner will be required, by the conditions for granting this exemption, to demonstrate that 

the risks due to uncontrollable high-thrust failure conditions on any airplane certificated under 

this exemption will not exceed those currently known and accepted for comparable existing 

transport-category airplanes. Making this a condition of this exemption, in combination with the 

condition that all practical actions be taken to eliminate or further reduce that risk, means that 

granting this exemption should not adversely affect and, in fact, should improve the average perflight-hour risk within the current transport-airplane fleet. 

For those existing transport airplanes re-evaluated to date, the conditions under which an 

uncontrollable high-thrust failure may jeopardize the safe operation of the airplane are limited to 

specific aborted takeoff or approach-and-landing scenarios. Given that these scenarios occur, 

there is still a low probability that a serious injury will result. This limited exposure, in 

conjunction with the historically low occurrence rates, makes this a relatively low risk per flight 

hour. 

It is the spectre of this low risk per flight hour accumulating indefinitely on many, if not most, 

existing and future transport airplanes that is the primary concern driving development of the 

FAA “Thrust Control Malfunction Airworthiness Program.” To date, corrective actions under 

14 CFR part 39 have been deemed warranted only when the uncorrected risks for a particular 

type design were considered significantly greater than those allowed by the conditions and 

limitations of this exemption. Given that these conditions and limitations require that any 

airplane certificated under this exemption have an uncontrollable high-thrust failure rate over 

three times better than the current fleet average, the impact of adding these GALP Model G280 

fleet hours to the overall transport fleet exposure should be insignificant. Furthermore, GALP is 

commiting to implement thrust-malfunction-accomodation logic within 4 years of the date of 

granting, which will further reduce that risk. If, as part of the “Thrust Control Malfunction 

Airworthiness Program,” the FAA determines that additional, generally applicable precautions 

must be taken, including perhaps some future introduction of this or other design features, these 

precautions will further minimize any cumulative-risk impact of granting this exemption. 
 7 

This exemption allows a somewhat greater hazard than full compliance with § 25.901(c). This is 

why the FAA intends to bring the transport fleet back into full compliance as soon as practicable. 

Nevertheless, the fact that the per-flight-hour risks associated with this non-compliance are low 

allows the FAA to develop a well-considered recovery program to assure that the solution does 

not introduce a problem worse than the one we are trying to solve, and that this recovery 

program is clearly in the public interest. 

The FAA agrees with GALP that mandating retrofit of the new thrust-malfunctionaccommodation logic is not warranted, as the initial G280 airplane design is expected to provide 

an acceptable level of safety. 

In consideration of the above, the FAA concludes that granting this time-limited exemption will 

not adversely affect safety. 

The Grant of Exemption 

In consideration of the foregoing, I find that a grant of exemption is in the public interest and 

will not adversely affect safety. Therefore, pursuant to the authority contained in 49 U.S.C. 

40113 and 44701, delegated to me by the Administrator, Gulfstream Aerospace LP (GALP) is 

granted an exemption from § 25.901(c) to the extent necessary to allow type certification of the 

Model G280 airplanes with Honeywell AS907 engines, without an exact showing of compliance 

with the requirements of § 25.901(c) or other applicable regulations as they relate to single 

failures resulting in uncontrollable high-thrust conditions. This exemption is subject to the 

following conditions and limitations: 

1. GALP must demonstrate, in accordance with an FAA-approved “Airworthiness Assessment 

and Risk Management Plan,” that all practicable actions have been taken to minimize the 

adverse effects on safety associated with granting this petition. These must include, but are 

not limited to, practical actions to eliminate or further reduce the risks by improving designs, 

procedures, training, and Instructions for Continued Airworthiness (ICA). 

2. GALP must demonstrate, in accordance with an FAA-approved “Airworthiness Assessment 

and Risk Management Plan,” that the risks associated with exempting the uncontrollable 

high-thrust failure condition from the single failure provisions of § 25.901(c) are no greater 

for the proposed Model G280 airplanes with Honeywell AS907 engines than those currently 

known and accepted for comparable airplanes within the current transport fleet. Acceptable 

risk for this provision can be characterized as: 

a. The airplane complies with § 25.901(c) for any foreseeable, uncontrollable, high-thrust 

failure conditions in flight, except possibly during approach below 400 feet; and 

b. The expected frequency of occurrence of the uncontrollable high-thrust failure condition 

is less than once per 10 million airplane operating hours. 
 8 

3. The following “Note” will be added to the airplane Type Certification Data Sheet for any 

airplane certificated under this exemption: 

The FAA has concluded that the occurrence of any uncontrollable high-thrust 

failure condition, or any of the associated causal failures listed within GALP 

Document (reference TBD), may endanger the safe operation of an airplane. 

Consequently, the FAA recommends that operators be encouraged to report any 

such failures in accordance with Title 14, Code of Federal Regulations 121.703 (c), 

125.409 (c), and 135.415 (c). 

In support of this “Note,” GALP must develop and obtain, prior to customer delivery, 

FAA approval of the GALP document referenced in the “Note.” This document lists 

those failures that can contribute to or cause an uncontrollable high-thrust failure 

condition covered by this exemption. This document will then be made available as part 

of the ICA. Further, the failures listed within this document will be added to the list of 

reportables under 14 CFR 21.3 for any airplane certificated under this exemption. 

4. No later than four years from this granting, for all airplanes to which this exemption applies, 

Gulfstream must: 

a. Obtain FAA approval of amended type designs incorporating thrust-malfunctionaccommodation logic that eliminates all noncompliant, uncontrollable, high-thrust 

failures, except for those due to failures within the airplane throttle system; 

b. Show that all new Model G280 production airplanes are equipped with the amended type 

designs approved to satisfy condition 4a or any subsequently approved thrustmalfunction-accommodation logic; and 

The granting of this exemption does not relieve any regulatory obligation to identify and correct 

unsafe conditions related to uncontrollable high-thrust failure conditions. 

Note: Additional background and guidance regarding these provisions are provided in FAA 

Letter 02-112-02, dated October 19, 2001. 

Issued in Renton, Washington, on December 19, 2011. 

 /s/ K. C. Yanamura 

K. C. Yanamura 

Acting Manager, Transport Airplane Directorate 

Aircraft Certification Service