Exemption No. 18102
UNITED STATES OF AMERICA DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADMINISTRATION
DES MOINES, WASHINGTON 98198
In the matter of the petition of
Gulfstream Aerospace Corporation for an exemption from § 25.841(a)(2) of title 14, Code of Federal Regulations
Regulatory Docket No. FAA-2018-0858
GRANT OF EXEMPTION
By letter dated September 10, 2018, Mr. Emery P. Wiltse, Director, ODA Enterprise
Administrator, Gulfstream Aerospace Corporation, 500 Gulfstream Road, Savannah, Georgia, 31408, petitioned the Federal Aviation Administration (FAA) for an exemption from the requirements of § 25.841(a)(2) of title 14, Code of Federal Regulations (14 CFR). This
exemption, if granted, would permit in-flight access to the baggage compartment above 40,000 feet, up to 45,000 feet altitude on Model GVII-G500 and GVII-G600 airplanes.
The petitioner requests relief from the following regulation:
Section 25.841(a)(2), amendment 25-87, states, the airplane must be designed so that occupants will not be exposed to a cabin pressure altitude that exceeds the following after decompression from any failure condition not shown to be extremely improbable:
(i) Twenty-five thousand (25,000) feet for more than 2 minutes; or (ii) Forty thousand (40,000) feet for any duration.
The petitioner supports their request with the following information:
This section quotes the relevant information from the petitioner’s request with minor edits for clarity. 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-2018-0858.
Petitioner’s Introduction
Gulfstream will certify the GVII-G500 and GVII-G600 to a maximum altitude of 51,000 feet. The GVII-G500 and GVII-G600 includes a Class B baggage compartment in the aft
section of the airplane. Under the current type certificate (TC), No. T00021AT, the access to the Class B baggage compartment is prohibited above 40,000 feet.
Title 14 CFR 25.841(a)(2), amendment 25-87, requires that the cabin altitude does not exceed the limits specified in the sub-paragraphs following decompression from any failure condition not shown to be extremely improbable, and § 25.841(a)(3), amendment 25-87, further requires that fuselage structure, engine, and systems failures be considered. An uncontained engine rotor failure (UERF) which punctures and/or tears the fuselage, creating a very large hole, is one of the engine failure scenarios considered for
compliance with these regulations.
In accordance with the provisions of 14 CFR 11.81, Gulfstream requests an exemption to § 25.841(a)(2), amendment 25-87, for the Model GVII-G500 and GVII-G600 airplanes and derivative models with regard to the effects of damage from UERF. This exemption is sought in accordance with FAA Policy No. ANM-03-112-16, Interim Policy on High Altitude Cabin Decompression (Reference Amendment 25-87), dated March 24, 2006. Gulfstream is seeking removal of the baggage compartment access altitude limitation up to 45,000 feet.
Reason that Gulfstream is Seeking Exemption
While the Model GVII-G500 and GVII-G600 airplanes are approved to operate at a maximum altitude of 51,000 feet pressure altitude, this petition seeks exemption from § 25.841(a)(2) for operating at altitudes above 40,000 feet and up to and including 45,000 feet. Should a UERF occur at an altitude of 45,000 feet, and if the engine debris were to strike the fuselage, it could potentially result in a hole in the fuselage. The hole size generated by engine debris could potentially exceed the maximum hole size for which the airplane’s environmental control systems are capable of maintaining allowable cabin altitudes resulting in exceeding the limits of § 25.841(a)(2), even when considering an emergency descent maneuver being performed following a UERF event.
Recognizing the possibility that such a UERF could result in rapid cabin decompression, Gulfstream has included a secondary pressure bulkhead in the model GVII-G500 and GVII-G600 design. This bulkhead is installed forward of the area exposed to potential UERF fragment impact. The area aft of this secondary pressure bulkhead is used as a baggage compartment.
The baggage compartment is accessible from the cabin through an internal baggage compartment door mounted on a track system that allows sliding motion parallel to the baggage compartment bulkhead. The baggage compartment can be intermittently accessed in flight. When the airplane is operating at or below the limiting altitude, the internal baggage compartment door normally remains closed when the compartment is not being accessed. The internal baggage door is required to remain closed at all times when operating above the limiting altitude.
Exemption from § 25.841(a)(2)(i) would allow the Model GVII-G500 and GVII-G600 cabin pressure altitude to exceed 25,000 feet for more than 2 minutes following a
decompression due to a UERF, should the event occur when the internal baggage compartment door is open. This duration would not exceed 3 minutes (ref. FAA Policy ANM-03-112-16) if a UERF event occurs while the airplane is at an altitude of 45,000 feet or lower. Gulfstream is seeking removal of the baggage compartment access altitude limitation up to 45,000 feet.
Petitioner’s Public Benefit/Public Interest Statement
Per 14 CFR 11.81(d), exempting the GVII-G500 and GVII-G600 airplanes from the requirements of § 25.841(a)(2), amendment 25-87, would benefit the general public, the travelling public, and the economy; and is therefore in the public interest. The following benefits would result from this exemption:
The new engine option and associated modifications necessary for the integration comply with the latest FAA requirements and therefore offer a significantly higher basic level of safety relative to previously certified transport category aircraft.
The Model GVII-G500 and GVII-G600 airplanes are equipped with PW800 series engines. When compared under similar conditions to the previous generation BR710 engine used on the earlier Gulfstream model airplanes, the PW800 series engine significantly reduces specific fuel consumption, NOx emissions, and visible smoke.
Maintaining higher, more efficient altitudes would result in reduced emissions and benefit the general public. Modifying the baggage compartment access altitude limitation would allow Model GVII-G500 and GVII-G600 operators full use of the baggage compartment at any approved flight altitude up to 45,000 feet. This would eliminate the need to remain below 40,000 feet or to descend to 40,000 feet when access to the baggage compartment is needed. This would allow continued operation at more efficient altitudes, resulting in reduced overall
emissions for any given flight segment. Modifying the baggage compartment access altitude limitation would improve operability of the Model GVII-G500 and GVII-G600 airplanes and incentivize business jet operators to replace older aircraft with Model GVII airplanes.
The current baggage compartment access altitude limitation adversely affects the ability of the Model GVII-G500 and GVII-G600 to compete with older aircraft and with current airplanes that do not have a similar limitation due to differing cabin configurations. Most of these other aircraft are produced by foreign manufacturers. Modifying the Model GVII-G500 and GVII-G600 baggage compartment access altitude limitation would improve the competitiveness of the national aviation industry. This would result in a positive effect on job creation and investment returns, a benefit to the general public.
Modifying the baggage compartment access altitude limitation would eliminate the need for Model GVII-G500 and GVII-G600 operators to remain below 40,000
feet or to descend to 40,000 feet when access to the baggage compartment is needed. This would enable the air traffic system to provide more capacity, and hence more aircraft separation and safety, without adversely affecting the safety of the passengers.
Petitioner’s Statement on Safety Aspects
The Model GVII-G500 and GVII-G600 airplanes fully comply with § 25.841(a)(2) for all applicable conditions other than UERF. Partial exemption is sought for a UERF only. Per 14 CFR 11.81(e), Gulfstream provides the following reasons why granting this exemption would not adversely affect safety provided by § 25.841(a)(2).
1. Flightcrew protection
In order to ensure the flightcrew will remain alert and be able to safely fly and land the airplane in the event of a cabin decompression, the Model GVII-G500 and GVII-G600 airplanes provide the flightcrew with quick-donning crew oxygen masks and a number of additional features to mitigate a possible cabin
decompression.
a. The Model GVII-G500 and GVII-G600 airplane flight manuals (AFM) require that crew masks be placed in the quick-donning position when operating above 25,000 feet, which allows them to be donned within 5 seconds. Furthermore, operators are required to comply with 14 CFR 91.211(b) “Supplemental Oxygen” and 14 CFR 135.89(b) “Pilot
Requirements: Use of Oxygen.” Compliance with the rule ensures that the flightcrew will retain the ability to safely operate the airplane following a decompression.
b. Furthermore, at least one flightcrew member must wear an oxygen mask when operating at altitudes above 35,000 feet to comply with 14 CFR 135.89(b)(3) and 14 CFR 91.211(b)(1)(ii). Compliance with the rule ensures that the flightcrew will retain the ability to safely operate the airplane following a decompression.
c. The Model GVII-G500 and GVII-G600 airplanes provide an aural warning and a visual red “Cabin Pressure Low” warning message via the crew alerting system (CAS) when cabin pressure altitude exceeds 8,000 feet (10,000 feet or higher for high altitude LFE [landing field elevation]). When these warnings are present, the Model GVII-G500 and GVII-G600 AFM instructs the flightcrew to don oxygen masks as a first and
immediate step prior to further procedural actions. Should a cabin decompression occur, the flightcrew will be immediately aware of the event and expected to take immediate corrective action. These operating procedures and airplane design features (aural/visual alerting) ensure the flightcrew will be made aware of a cabin decompression and will be
capable of performing their duties to initiate an emergency descent to a flight altitude where pressurization is not required.
d. As an additional protection against loss of airplane control due to crew incapacitation, the Model GVII-G500 and GVII-G600 airplanes’ autopilot includes an “Emergency Descent Mode,” which will automatically initiate an emergency descent maneuver to a safe altitude (including a 90° heading change to exit the airway) when a high cabin pressure altitude is detected. This added safety feature provides a means to survive a condition where both flightcrew members are incapacitated – though this should never occur per the previously cited operating requirements.
e. Pilots attending GVII-G500 and GVII-G600 initial and recurrent training receive academic instruction on the oxygen system and crew oxygen masks installed in the airplane. Additionally, simulator training for the pilots includes at least one in-flight emergency scenario requiring the pilots to quickly don their oxygen mask and perform an emergency descent.
In summary, these Model GVII-G500 and GVII-G600 aural/visual alerting features and operating requirements ensure protection for the crew and provide a level of safety at least equal to that provided by full compliance with § 25.841(a)(2).
2. Occupant survivability
Airplane structural integrity has been demonstrated for cabin decompressions with the internal baggage compartment door both open and closed. In order to protect the cabin occupants from the effects of hypoxia, the Model GVII-G500 and GVII-G600 airplanes provide supplemental oxygen via the passenger oxygen system. This system is compliant with the requirements of § 25.1447(c) and automatically deploys the passenger masks prior to the cabin altitude reaching 14,750 feet (± 250 feet) for LFE ≤ 14,000 feet, and 15,750 feet (± 250 feet) for 14,000 < LFE ≤ 15,000 feet. Additionally, Gulfstream has demonstrated the emergency descent capability of the Model GVII-G500 and GVII-G600 airplanes by flight test, from the maximum certified operating altitude of 51,000 feet to a safe altitude of 15,000 feet.
Occupant survivability in the event of a rapid cabin decompression at altitudes above 40,000 feet merits further consideration, particularly in the event that an occupant is unable to make use of the supplemental oxygen provided by the passenger oxygen system.
The FAA addressed this issue in Policy No. ANM-03-112-16, Interim Policy on High Altitude Cabin Decompression (Reference Amendment 25-87), dated March 24, 2006. This interim policy was established to provide guidelines for granting exemptions from the requirements of § 25.841(a)(2), amendment 25-87, with regard to the effects of damage from a UERF.
The policy described in FAA Policy No. ANM-03-112-16 was originally intended for application on airplanes with wing-mounted engines, which due to their configuration are unable to provide mitigating features such as the secondary pressure bulkhead on the Model GVII-G500 and GVII-G600 airplanes.
For these airplanes, which are less protected from the effects of UERF than the model GVII, FAA Policy No. ANM-03-112-16 established the following alternative limits to cabin pressure altitude exposure.
Cabin Pressure Altitude (feet) Maximum Total Exposure Time (minutes)
Above 45,000 0
Above 40,000 1
Above 25,000 3
Above 10,000 6
FAA Policy No. ANM-03-112-16 explains these alternative limits were based on a physiological model that approximates the blood saturation level of oxygen and incorporates known phenomenological relationships that describe the respiratory cycle, lung mechanics, lung, venous and arterial blood flows and calculates trans-alveolar oxygen. The intent of these limits is to ensure that permanent harm to occupants is unlikely in the event of a cabin decompression, even if an occupant is unable to use supplemental oxygen.
Figure 1: Emergency Descent Profile G500
Figure 2: Emergency Descent Profile G600
UERF events are very rare. A simple calculation shows that grouping all engines and transport category airplanes together yields an average probability of a UERF at cruise
altitude of approximately 1x10-7 per engine hour. New engine designs appear to reduce
this probability by order of magnitude. The Aviation Rulemaking Advisory Committee’s Mechanical Systems Harmonization Working Group (MSHWG) report on § 25.841(a) shows that there are no fatalities from hypoxia due to in-flight decompression events as envisioned by amendment 25-87. The data indicates that decompression is not a
significant cause of fatalities.
Gulfstream performed a decompression analysis for an emergency descent after UERF at 45,000 feet. Gulfstream used a 17-second pilot reaction time, consistent with guidelines established with section 8(d)(2) of Advisory Circular (AC) 20-128A, Design
Considerations for Minimizing Hazards Caused by Uncontained Turbine Engine and Auxiliary Power Unit Rotor Failure, dated March 25, 1997. The emergency descent profile is shown above.
The analysis shows that:
For the Model GVII-G500 – The cabin altitude is above 25,000 feet for 176 seconds, above 40,000 feet for 48 seconds, and reaches a maximum of 45,000 feet.
For the Model GVII-G600 – The cabin altitude is above 25,000 feet for 169 seconds, above 40,000 feet for 48 seconds, and reaches a maximum of 45,000 feet.
Therefore, this emergency descent from 45,000 feet meets the alternative limits prescribed in FAA Policy No. ANM-03-112-16.
In addition, Gulfstream performed a Depressurization Exposure Integral (DEI)
calculation, and the resulting values for the Model GVII-G500 and GVII-G600 airplanes are below the recommended values in the MSHWG Report for § 25.841(a)(2) and (a)(3). These maximum allowable values are:
DEI 30 < 2160 mmHg-sec DEI 60 < 12000 mmHg-sec
3. Probability of occurrence
The altitude exposure discussed in the preceding Occupant Survivability section can only occur as a result of an extremely improbable series of events.
The Model GVII-G500 and GVII-G600 airplanes are equipped with Pratt & Whitney Canada PW800 series turbofan engines. The PW814/815 engine shares the same common core with the PW1500G and PW1900G series engines. These common cores incorporate decades of accumulated knowledge in materials, design, manufacturing, and maintenance practices that minimize the probability of uncontained failures.
There have been no uncontained rotor core events on the PW1500G/PW1900G/PW800 engines.
Based on the accumulated cycles with no recorded events, that study derived a failure rate of 2.5E-8 disk failures per engine cycle for third generation engines.
Using the accepted UERF models and assessment methods described in FAA AC 20-128A, Gulfstream has determined that the Model GVII-G500 and GVII-G600 baggage compartment pressure vessel exposure to intermediate and large
fragments is limited to the fan, two LP Boost stages, and HPC1, HPC2, HPC3, and HPC4 stages of the engines. Only 7 out of 22 engine stages (including covers) on each engine therefore, have the potential to cause sufficient damage to result in a sudden decompression.
Only a subset of the potential fragment trajectories from these engine stages can impact the baggage compartment.
Should a UERF occur on a model GVII-G500 or GVII-G600 airplane releasing an intermediate or large disk fragment, there is only a 3.38% chance that the
fragment will be released on a trajectory that impacts the pressure vessel. Though access to the baggage area in flight is necessary to allow full use of the cabin volume, the area is only intermittently accessed for placement or retrieval of items. The door is kept closed at all times when the baggage compartment is not being accessed. This is enforced by specific indications in the CAS and related operating limitations in the AFM, and incentivized by the fact that keeping the door open detracts from passenger comfort, as it increases cabin noise levels. Currently the Model GVII-G500 and GVII-G600 CAS presents a “caution” (amber) message to the flightcrew whenever the baggage compartment door is not closed and the airplane is above 40,000 feet altitude. The associated crew action is to close the door.
Should this exemption be granted, Gulfstream will increase the FAA AFM limitation in section 01-52-50 for baggage compartment access from 40,000 feet to 45,000 feet. The current model GVII-G500 and GVII-G600 CAS (amber) message to the flightcrew would be changed to activate if the baggage compartment door is not closed at altitudes above 45,000 feet.
The baggage compartment door remains closed for the vast majority of the flight duration. If a UERF were to occur and cause significant damage to the baggage compartment, depressurizing it, this would most likely occur while the door is closed and would therefore not result in decompression of the main area of the cabin. Gulfstream conservatively estimates that the baggage compartment will be accessed for no more than 10% of the flight duration at altitude.
These factors can be brought together to estimate the probability that a UERF would actually result in rapid decompression:
Probability of UERF disk failure (intermediate or large fragment):
The probability of a sudden decompression due to a UERF on the Model GVII-G500 or GVII-G600 airplane is extremely improbable, on the order of 3x10-11 per
flight hour. This is over 30 times less likely that the accepted failure rate for catastrophic system failure conditions of 1x10-9 per flight hour. Note that the
probability of debris impact to the pressure vessel alone, regardless of flight phase and baggage door status, is also extremely improbable.
4. Other consideration
FAA Exemption No. 17727 to § 25.841(a)(2) has been recently granted for the GVI to allow Class B baggage compartment access up to 45,000 feet.
Operation Outside the United States
The European Aviation Safety Agency (EASA) Certification Standard (CS) 25.841 regulation is not currently harmonized with 14 CFR 25.841.
Regardless of EASA requirements, per 14 CFR 11.81(h), Gulfstream requests consideration be given to extend this exemption for operation outside of the United States. Granting this extension of privileges will allow for operations based within foreign countries having bilateral agreements with the United States accepting 14 CFR part 25 as their airworthiness standard for transport category airplanes. Gulfstream believes that limiting this exemption to use within the United States would put unfair restrictions on the marketability of this airplane.
Petitioner’s Conclusion
Gulfstream believes that the above arguments favor an exemption from § 25.841(a)(2) that would allow the access to the GVII-G500 and GVII-G600 Class B baggage
compartment up to 45,000 feet. In addition, Gulfstream believes that an exemption is in the public interest and will provide a level of safety consistent with the current part 25 regulations.
Federal Register publication:
The FAA has determined that good cause exists for waiving the requirement for Federal Register publication for public comment because the public comment is unnecessary, in that the request is nearly identical in all material respects to previously granted exemptions for which no comment was received; and the exemption, if granted, would not set a precedent.
The FAA’s analysis is as follows:
The FAA’s analysis of this petition is based on both the original petition and additional proprietary information received from Gulfstream on October 17, 2018.
Gulfstream requests relief from § 25.841(a)(2), which specifies that cabin pressure altitude may not exceed 25,000 feet for more than 2 minutes, nor exceed 40,000 feet for any time, after decompression from any failure condition not shown to be extremely improbable. A grant of exemption from these regulations for certain engine failures would allow passengers and crew to access the baggage compartment at airplane altitudes above 40,000 feet, up to a maximum altitude of 45,000 feet; improve performance; and avoid airspace congestion.
Removing the current baggage-compartment-access altitude limitation (40,000 feet) could improve operability of the Model GVII-G500 and GVII-G600 airplanes and avoid airspace congestion. Currently, to access the baggage compartment according to the regulations, an operator must first descend to 40,000 feet. After the baggage compartment access is completed, the airplane can climb back to a more efficient altitude. This maneuver increases fuel usage and engine emissions, and adds to airspace congestion.
Gulfstream states that the baggage-compartment-access altitude limitation adversely affects the ability of the Model GVII-G500 and GVII-G600 airplanes to compete with older airplanes, and with current airplanes that do not have a similar limitation due to differing cabin configurations. Foreign manufacturers produce most of these other airplanes.
Conformance with applicable FAA policy
The FAA reviewed this petition in the context of the Aviation Rulemaking Advisory Committee (ARAC) Mechanical Systems Harmonization Working Group (MSHWG) final report on
§ 25.841(a)(2) and (3), dated August 2003, and FAA Policy Memorandum ANM-03-112-16, Interim Policy on High Altitude Cabin Decompression (Reference Amendment 25-87), dated March 24, 2006. The interim policy applies only to those decompression events that are due to uncontained engine rotor failure (UERF). The interim policy is based on data from research on the response of humans and other primates to changes in ambient pressure. Evaluation of this data indicates a direct correlation between the alveolar pressure of oxygen time integral and the likelihood of fatalities or permanent physiological damage to those exposed to such pressure changes. That is, as the value of the integral increases, the likelihood of fatalities or permanent physiological damage also increases. However, to simplify, the FAA accepted “pass/fail criteria,” and Policy Memorandum ANM-03-112-16 uses a table of altitudes and cumulative exposure times in lieu of the pressure-time integral. It is important to note that the values of altitude and time in the table, and the results of the pressure-time integral method, agree. Accordingly, Policy Memorandum ANM-03-112-16 focuses on minimizing the likelihood that, if a person is exposed to high-altitude cabin pressure from any failure not shown to be extremely improbable, they will suffer permanent physiological damage. To analyze petitions for
exemption from § 25.841(a)(2), the FAA requires information about emergency descent rates, design features that increase such rates, other design features that offset the inherent increased risk of exposure to high-altitude cabin pressure, and operational procedures.
As stated in Policy Memorandum ANM-03-112-16, the FAA acknowledges a lack of relevant data on the effects of exposure to high-altitude cabin pressure following decompression and, particularly, those effects on people of various ages, and on people with circulatory or respiratory diseases or certain other medical conditions.
Gulfstream provided data per the guidance contained in Policy Memorandum ANM-03-112-16, which the FAA has relied upon for all previous petitions for exemption to the associated
regulations. This data indicates that the Model GVII-G500 and GVII-G600 airplanes are able to meet all of the exposure limits provided in the policy (i.e., cabin pressure altitude does not exceed 45,000 feet; cabin pressure at and above 40,000 feet pressure altitude exposure of no more than 1 minute; and, cabin pressure above 25,000 feet for no more than 3 minutes) when cruising at 45,000 feet.
Review of historical data and research
The FAA reviewed databases from the National Aviation Safety Data Analysis Center (now called the Aviation Safety Information Analysis and Sharing (ASIAS) database), containing data gathered from 1959 to 2006. Within that time, the data reveals approximately 3,000 instances of cabin-pressure loss. System failures (e.g., cabin-pressurization-controller failures, valve failures, etc.) and structural failures (e.g., door-seal failures) have caused the vast majority of these instances, typically recognized at low altitude within a few minutes after takeoff. Pilot error also contributed to the number of events. The majority of these events have not subjected the
occupants to exposures above 25,000 feet (an altitude considered physiologically significant). The cabin pressure altitude in most events did not exceed 15,000 feet (the cabin pressure altitude at which passenger oxygen masks are deployed).
Similarly, UERF events are very rare. A simple calculation shows that grouping all engines and transport airplanes together yields an average probability of a UERF at cruise altitude of
approximately 1x10-7 per engine hour. New engine designs appear to reduce this probability by
an order of magnitude. The FAA found, as noted in the MSHWG report on § 25.841(a), that no fatalities from hypoxia were due to in-flight rapid decompression events as envisioned by
amendment 25-87. The data indicates that decompression is not a significant cause of fatalities. It is because these events are so rare that the FAA considers the risk of flight above 40,000 feet pressure altitude to be acceptable.
Holes from UERF
Gulfstream evaluated the size of holes in the fuselage and wing in this scenario, and provided the results in their petition and in proprietary supplemental material. The FAA evaluated
Gulfstream’s approach for determining the size of holes in the fuselage and wings caused by UERF. Gulfstream’s approach followed FAA regulatory guidance contained in AC 25-20, Pressurization, Ventilation, and Oxygen Systems Assessment for Subsonic Flight Including High Altitude Operation, dated September 10, 1996; and AC 20-128A, Design Considerations for Minimizing Hazards caused by Uncontained Turbine Engine and Auxiliary Power Unit Rotor Failure, dated March 25, 1997.
Use of supplemental oxygen
As discussed in further detail below, the FAA analyzed the Gulfstream petition in the context of the MSHWG recommendations, the part 25 requirements pertaining to supplemental oxygen, and certain technical standards for supplemental-oxygen equipment.
Section 25.1441(d) requires approval of oxygen equipment for airplanes that are approved to operate above 40,000 feet altitude. Section 25.1443 specifies the minimum mass flow of supplemental oxygen for flightcrew and passenger oxygen systems up to a cabin altitude of 40,000 feet. Part 25 does not contain standards for oxygen systems above 40,000 feet. However, FAA technical standard orders (TSO) provide requirements for diluter demand
pressure-breathing regulators (TSO-C89a) and demand oxygen masks (TSO-C78a) up to 45,000 feet. In addition, SAE International Aerospace Standard AS8027 provides specifications for diluter demand pressure-breathing regulators up to 45,000 feet.
Oxygen-system protection above 40,000 feet requires pressure-breathing equipment. Flightcrew pressure-breathing equipment requires training to ensure effective use. Pressure breathing requires physical effort to exhale and minimum effort to inhale. This reversal of the normal breathing cycle can lead to hyperventilation. Training of passengers to use pressure-breathing equipment safely is considered impractical. The FAA determined that an acceptable means of compliance for the fixed- and portable-oxygen systems used by flight attendants and passengers would be to install oxygen equipment that is certificated to 40,000 feet, and limit exposure to the reduced pressure environment above 40,000 feet via airplane-descent performance. Ultimately, occupant survival during a decompression event depends upon a swift descent to a lower altitude and Gulfstream followed the guidelines explained in FAA Policy Memorandum ANM-03-112-16 to minimize the exposure to high altitude.
Conclusion of FAA analysis
Permitting airplanes to fly above 40,000 feet does offer real and tangible benefits to the
aerospace industry, the travelling public, and the United States economy by reducing congestion, improving fuel economy, and reducing pollution. If compliance with § 25.841, amendment 25-87, were to limit airplane operations to a maximum altitude of 40,000 feet, it would impose a significant disadvantage on newly designed airplanes that have many safety advantages over older airplanes currently allowed to operate at higher altitudes. This would delay the introduction of these airplanes and the benefits of their advanced technology. The Model GVII-G500 and GVII-G600 airplanes are approved for flight to a maximum altitude of 51,000 feet, but access to the baggage compartment is currently restricted to 40,000 feet altitude and below. Gulfstream’s request is to allow access to the baggage compartment up to a flight altitude of 45,000 feet for a short period of time. The necessity to descend from 51,000 feet to 40,000 feet, to access the baggage compartment and then climb back to cruise altitude, incurs additional fuel consumption and engine emissions, and represents an inconvenience to the air traffic system.
The Model GVII-G500 and GVII-G600 designs include an “Emergency Descent” mode, which will automatically initiate an emergency descent maneuver to a safe altitude (including a 90
heading change to exit the airway) when a high cabin pressure altitude is detected. This added safety feature provides a means to survive a condition where both flightcrew members could be initially incapacitated.
The FAA finds that the effects of the decompression exposure, as requested by Gulfstream, follows the exposure duration guidelines explained in FAA Policy Memorandum ANM-03-112-16 and accepted on previous grants of exemption. This is consistent with the goal of FAA Policy Memorandum ANM-03-112-16, which is to ensure that the decompression exposure does not result in permanent physiological harm to healthy individuals.
Based upon an evaluation of the data and analysis Gulfstream provided, the FAA determined that the petitioner does have sufficient justification for a grant of exemption from § 25.841(a)(2) for certain engine failures up to an operating altitude of 45,000 feet. This permits Gulfstream access to the baggage compartment up to an operating altitude of 45,000 feet. The petitioner met all of the criteria in FAA Policy Memorandum ANM-03-112-16 when operating at an altitude of 45,000 feet. A grant of exemption from § 25.841(a)(2)(ii) will permit cabin pressure altitude to exceed 40,000 feet for 1 minute (but not to exceed 45,000 feet for any duration), after
decompression from any UERF condition not shown to be extremely improbable, during the time that the baggage compartment is being accessed up to an operating altitude of 45,000 feet. A grant of exemption from § 25.841(a)(2)(i) permits cabin pressure altitude to exceed 25,000 feet for more than 2 minutes (but not more than 3 minutes), after decompression from any UERF condition not shown to be extremely improbable, allowing time for the airplane to descend from an altitude of 45,000 feet to 25,000 feet.
A grant of exemption is predicated on the requirement that Gulfstream successfully demonstrates compliance to §§ 25.1441, 25.1443, 25.1445, 25.1447, and 25.1449 for all supplemental oxygen systems used on the Model GVII-G500 and GVII-G600.
The FAA’s Decision
In consideration of the foregoing, I find that a grant of exemption is in the public interest. Therefore, pursuant to the authority contained in 49 U.S.C. §§ 40113 and 44701(f) delegated to me by the Administrator, I grant Gulfstream Aerospace Corporation an exemption from 14 CFR 25.841(a)(2) to the extent necessary to allow occupants of the Model G500 and GVII-G600 airplanes access to the baggage compartment at altitudes up to 45,000 feet pressure altitude.
Conditions and Limitations
This exemption is subject to the following conditions:
1. The Model GVII-G500 and GVII-G600 airplane flight manuals (AFM) must specify that the cruise maximum indicated operating pressure altitude for passenger access to the Class B cargo compartment is 45,000 feet.
2. The Model GVII-G500 and GVII-G600 AFM must contain applicable flightcrew procedures for a rapid decompression event. The section of the AFM that pertains to actions in the event of a decompression must state that the flightcrew should initiate a descent at the maximum rate of descent and safe descent speed, which is typically the maximum operating speed (VMO/MMO), assuming structural integrity of the airplane.
3. Gulfstream Aerospace Corporation must submit certification flight-test data for the Model GVII-G500 and GVII-G600 airplanes that corroborates the descent profiles used in the analysis to show that, after decompression at an airplane indicated operating pressure altitude of 45,000 feet and with the Class B cargo compartment door open, the cabin pressure altitude will not exceed 25,000 feet for more than 3 minutes, or 40,000 feet for more than 1 minute.
Issued in Des Moines, Washington, on January 29, 2019. /s/
Victor Wicklund
Manager, Transport Standards Branch Policy and Innovation Division Aircraft Certification Service
