+---------------+--------------------+--------------------------------+
| *             | **DISPOSITION OF   | **Disposition:**               |
| *Commenter:** | PUBLIC COMMENTS ON |                                |
|               | DRAFT POLICY       |                                |
|               | STATEMENT ANM-     |                                |
|               | 03-112-16, INTERIM |                                |
|               | POLICY ON HIGH     |                                |
|               | ALTITUDE CABIN     |                                |
|               | DECOMPRESSION      |                                |
|               | INTERIM POLICY:    |                                |
|               | Ref Amendment      |                                |
|               | 25-87**            |                                |
|               |                    |                                |
|               | **Comment:**       |                                |
+---------------+--------------------+--------------------------------+
| # **Boeing:** | Boeing requested   | [FAA response:]{.underline}    |
|               | the following      |                                |
|               | changes            | \(1\) Industry asked FAA to    |
|               | (Summarized). In   | provide interim policy to      |
|               | addition, Boeing   | permit the development and     |
|               | provided more      | certification of new transport |
|               | detailed changes   | category airplanes. FAA agrees |
|               | to text.           | that wherever possible the     |
|               |                    | regulations should be          |
|               | [Requested         | performance based. However,    |
|               | cha                | this policy is unique in that  |
|               | nges:]{.underline} | (a) it states that an          |
|               |                    | applicant must follow the      |
|               | \(1\) Much of the  | exemption process and (b) it   |
|               | policy is          | allows manufacturers to        |
|               | unnecessarily      | observe how the FAA technical  |
|               | prescriptive in    | specialist will evaluate an    |
|               | nature and should  | applicant's petitions for      |
|               | be replaced with   | exemption. As such, it permits |
|               | performance based  | industry with unprecedented    |
|               | requirements.      | access to the process.         |
|               |                    | Performance-based standards    |
|               | \(2\) Inclusion of | state regulatory requirements  |
|               | any physiological  | in terms of objective safety   |
|               | considerations     | performance rather than        |
|               | should be deleted. | specific design                |
|               | As proposed in the |                                |
|               | policy, these are  | requirements. However there    |
|               | more stringent     | are circumstances where FAA    |
|               | than the current   | regulations need to be more    |
|               | rule as well as    | specific. Historical precedent |
|               | proposals          | has been established in        |
|               | currently being    | previous published material    |
|               | developed by the   | where FAA has acknowledged     |
|               | ARAC working       | that, "*Performance-based      |
|               | group. Any policy  | standards are desirable from   |
|               | to require that    | the*                           |
|               | the physiological  |                                |
|               | considerations be  | *standpoint that they offer    |
|               | met should be      | the manufacturer maximum       |
|               | deferred until     | flexibility in designing       |
|               | completion of      | equipment or systems to comply |
|               | ARAC.              | with the regulations. They     |
|               |                    | can, however, be difficult to  |
|               | \(3\) The          | develop, particularly when     |
|               | attachment on      | involved with human            |
|               | physiological      | performance, as is the case    |
|               | considerations     | with emergency evacuation      |
|               | should be deleted. | regulations*."                 |
|               |                    |                                |
|               |                    | FAA believes that human        |
|               |                    | physiology regarding high      |
|               |                    | altitude decompression falls   |
|               |                    | into this category.            |
|               |                    | Furthermore, as the commenter  |
|               |                    | is aware, there is much        |
|               |                    | controversy on the subject of  |
|               |                    | high altitude human            |
|               |                    | physiology.                    |
|               |                    |                                |
|               |                    | While FAA's goal is to seek a  |
|               |                    | performance based rule as an   |
|               |                    | outcome of the current ARAC    |
|               |                    | rulemaking activity involving  |
|               |                    | the Mechanical Systems         |
|               |                    | Harmonization Working Group    |
|               |                    | (MSHWG), FAA declines making   |
|               |                    | this change in the interim     |
|               |                    | policy.                        |
|               |                    |                                |
|               |                    | \(2\) FAA disagrees that the   |
|               |                    | physiological considerations   |
|               |                    | in the policy are more         |
|               |                    | stringent that the current     |
|               |                    | rule. The current rule         |
|               |                    | restricts cabin altitude to    |
|               |                    | 40,000 feet while this policy  |
|               |                    | permits a maximum cabin        |
|               |                    | altitude to 45,000 feet. FAA   |
|               |                    | considers this to be relieving |
|               |                    | in nature. However, FAA does   |
|               |                    | agree that the specific        |
|               |                    | functional relationship in the |
|               |                    | means of compliance (i.e.,     |
|               |                    | transform function from cabin  |
|               |                    | total pressure to approximate  |
|               |                    | alveolar partial pressure of   |
|               |                    | oxygen) is more                |
|               |                    | conservative/restrictive than  |
|               |                    | the means discussed within the |
|               |                    | ARAC. FAA believes that this   |
|               |                    | is justified until further     |
|               |                    | testing is accomplished that   |
|               |                    | yields data to validate the    |
|               |                    | functional relationship. It    |
|               |                    | should be noted that FAA has   |
|               |                    | revised the interim policy to  |
|               |                    | eliminate the need to          |
|               |                    | calculate the pressure-time    |
|               |                    | integral. FAA has provided a   |
|               |                    | simple table indicating the    |
|               |                    | maximum time exposure to       |
|               |                    | altitudes. This approach has   |
|               |                    | been coordinated within the    |
|               |                    | FAA including the office of    |
|               |                    | aerospace medicine.            |
|               |                    |                                |
|               |                    | \(3\) FAA disagrees. FAA       |
|               |                    | believes that it is our        |
|               |                    | responsibility to the          |
|               |                    | traveling public to provide    |
|               |                    | them with an explanation as to |
|               |                    | why we believe the course of   |
|               |                    | action outlined in the memo    |
|               |                    | results in reasonable          |
|               |                    | passenger safety while         |
|               |                    | enabling industry to develop   |
|               |                    | and operate new airplanes      |
|               |                    | above 40,000 feet.             |
+---------------+--------------------+--------------------------------+
| **[UK         | UK CAA provided    | [FAA response:]{.underline}    |
| CAA:]{        | detailed comments  | (1) FAA and other authorities  |
| .underline}** | as follows:        | face the same challenge in     |
|               |                    | this regard. Transport Canada  |
|               | \(1\) CAA is aware | and the Brazilian authority    |
|               | of the fundamental | are other aviation authorities |
|               | importance of this | that have adopted these FAA    |
|               | issue and the      | requirements as conditions for |
|               | power of the       | the operation of airplanes at  |
|               | precedents that    | altitudes up to 51, 000 feet.  |
|               | might be set in    | Some authorities that have not |
|               | applying this      | adopted Amendment 25-87 do     |
|               | policy. Under      | have some of their             |
|               | \'Interim Policy\' | manufacturer's meet special    |
|               | on page 2 it       | conditions similar to those    |
|               | states that the    | requirements that the FAA has  |
|               | *\"intent is not   | imposed on executive business  |
|               | to pre-empt the    | jets for high altitude flight. |
|               | ARAC activity.\"*  | However, some authorities have |
|               | From our           | adopted a philosophy that      |
|               | understanding of   | sudden loss of cabin pressure  |
|               | the difficulties   | need not be considered in the  |
|               | the Mechanical     | design of an airplane and      |
|               | Systems            | impact on occupants per 25.841 |
|               | Harmonization      | based on the rarity of         |
|               | Working Group      | uncontained engine failures,   |
|               | (MSHWG) is         | hence a probabilistic          |
|               | experiencing it is | approach. FAA philosophy does  |
|               | difficult to see   | not permit the use of          |
|               | how this intent    | probability as the sole means  |
|               | can be met. If     | of compliance to 25.841. FAA   |
|               | issued, this       | philosophy continues to be     |
|               | policy would be    | that we require US             |
|               | used for the A380, | manufacturers, and foreign     |
|               | B7E7, and other    | manufacturer's that seek FAA   |
|               | aircraft types for | certification to consider such |
|               | some years until   | failures in their design and   |
|               | the MSHWG report   | ensure that their airplane     |
|               | is turned into a   | design be robust enough to     |
|               | rule.              | retain the capability to       |
|               |                    | safely perform a speedy        |
|               | \(2\) "There       | descent to lower altitudes to  |
|               | appear to be       | ensure a reasonable level of   |
|               | significant        | protection to the occupants.   |
|               | difficulties faced |                                |
|               | by the MSHWG in    | \(2\) There is some data       |
|               | formulating an     | available from human and       |
|               | acceptable         | non-human primate altitude     |
|               | regulatory         | chamber studies. FAA has       |
|               | standard as there  | utilized this data and         |
|               | appears to be a    | believes that we have          |
|               | significant lack   | formulated conservative limits |
|               | of data available  | that will enable safe high     |
|               | and this might     | altitude flight during the     |
|               | force invalid      | interim period until a final   |
|               | assumptions and/or | rule is promulgated. FAA may   |
|               | extrapolations to  | seek funding to undertake an   |
|               | be made.           | additional high altitude       |
|               |                    | chamber study as recommended   |
|               | \(3\) It is noted  | in the MSHWG report.           |
|               | that on pages 3    |                                |
|               | and 4, Technical   | \(3\) See response (2) above.  |
|               | Issues there is a  | In addition, FAA has revised   |
|               | very honest and    | the interim policy to          |
|               | accurate           | eliminate the need to          |
|               | assessment of the  | calculate the pressure-time    |
|               | lack of medical    | integral. FAA has provided a   |
|               | corroboration for  | simple table indicating the    |
|               | the development of | maximum time exposure to       |
|               | an acceptable      | altitudes. This approach has   |
|               | exposure to high   | been coordinated within the    |
|               | altitude           | FAA including the office of    |
|               | conditions.        | aerospace medicine.            |
|               | Because of that    |                                |
|               | lack of data we    | \(4\) See response (2) and (3) |
|               | find it difficult  | above.                         |
|               | to accept that the |                                |
|               | pressure-time      | \(5\) The FAA's view is that   |
|               | integral method is | it is not possible to ensure a |
|               | valid, and we urge | zero level of risk to any      |
|               | the FAA to         | occupant following a rapid     |
|               | reconsider its     | decompression. There is not a  |
|               | position on this.  | "new level of risk;" there     |
|               |                    | always was a level of risk     |
|               | \(4\) At the top   | associated with such a         |
|               | of page 5 it is    | failure. FAA was not aware of  |
|               | stated that a      | the level of risk when we      |
|               | research program   | promulgated Amendment 25-87    |
|               | to gain additional | and stated the goal which was  |
|               | substantive data   | to ensure that even those      |
|               | will permit a      | individuals that were not able |
|               | realistic          | to properly don an oxygen mask |
|               | numerical          | would be protected from any    |
|               | appraisal of the   | permanent physiological harm.  |
|               | severity of the    | It is a laudable goal, but one |
|               | decompression      | that cannot be practically     |
|               | environment. CAA   | achieved.                      |
|               | agrees with this   |                                |
|               | point and believes | \(6\) See response (5) above.  |
|               | that the FAA       |                                |
|               | should obtain such | \(7\) At this time, FAA is     |
|               | data as a          | waiting for recommendations    |
|               | prerequisite to    | from the Powerplant            |
|               | allowing this      | Installation Harmonization     |
|               | policy to proceed. | Working Group (PPIHWG) on the  |
|               |                    | best model of the engine       |
|               | \(5\) CAA fully    | failure threat. With regard to |
|               | supports the page  | the rulemaking activity, our   |
|               | 5, 2nd bullet      | intent is to use the           |
|               | statement made     | recommendations from both      |
|               | under Exemption    | MSHWG and the PPIHWG working   |
|               | Process that \"The | groups. PPIHWG should provide  |
|               | applicant should   | a suitable means to determine  |
|               | also show why      | the engine threat              |
|               | granting such an   | (distribution of uncontained   |
|               | exemption would    | engine fragments,              |
|               | not adversely      | trajectories, etc.) and the    |
|               | affect safety.\"   | MSHWG for the resulting impact |
|               | The effect on      | to the cabin environment. For  |
|               | occupant safety    | the period of time until the   |
|               | rests on the       | rulemaking is completed the    |
|               | \'safe exposure    | assumption that the FAA        |
|               | time\' and if this | recommends is that the         |
|               | isn\'t established | manufacturer evaluate a rapid  |
|               | with a high degree | decompression as noted in the  |
|               | of confidence then | MSHWG ARAC WG report.          |
|               | allowing higher    |                                |
|               | altitude           | \(8\) FAA concurs with the     |
|               | operations,        | intent of the first comment.   |
|               | without effective  | However, the MSHWG has         |
|               | mitigations, would | completed their work and       |
|               | introduce a new    | recommended a new regulation   |
|               | hazardous, or even | and new guidance material for  |
|               | catastrophic,      | the cabin environment          |
|               | failure condition. | following a rapid              |
|               | Considering the    | decompression caused by an     |
|               | shared goal of     | uncontained engine rotor       |
|               | reducing the fatal | burst. FAA has no plans at     |
|               | accident rates the | this time to revise this       |
|               | introduction of a  | interim policy. Our position   |
|               | new risk, rather   | is that the interim policy     |
|               | than a lowered     | will be replaced by the new    |
|               | risk or equivalent | rule.As noted in the interim   |
|               | risk, must be      | policy, "This policy, while    |
|               | seriously          | limited in scope, is           |
|               | considered by the  | consistent with the final ARAC |
|               | FAA at a strategic | recommendation and will serve  |
|               | level.             | as policy until a new          |
|               |                    | regulatory standard is         |
|               | \(6\) The page 5   | issued."                       |
|               | Exemption Process  |                                |
|               | statement quoted   | Regarding the comment *"...to  |
|               | above continues by | make Petitioners aware that    |
|               | stating \"\...the  | approvals granted from use of  |
|               | applicant should   | this policy might be affected  |
|               | provide sufficient | or even rescinded should an    |
|               | mitigation         | unsafe condition be identified |
|               | strategies that    | from the MSHWG studies*." FAA  |
|               | focus on those     | believes that applicants for   |
|               | design features    | certification and those that   |
|               | that provide some  | petition for an exemption are  |
|               | means to offset    | aware that FAA may issue       |
|               | the inherent       | airworthiness directives or    |
|               | increased risk     | take other appropriate action  |
|               | associated with    | as warranted by safety         |
|               | exposure of        | concerns.                      |
|               | occupants to high  |                                |
|               | altitude           | Regarding the comment          |
|               | conditions.\" This | "*Because of the lack of       |
|               | statement appears  | physiological data at high     |
|               | to accept that a   | altitudes we find it difficult |
|               | new inherent risk  | to accept the pressure-time    |
|               | would exist (see   | integral method is valid, we   |
|               | above comment),    | urge the FAA to reconsider its |
|               | and the only       | position on this. We support   |
|               | mitigations or     | FAA obtaining additional data  |
|               | design features    | as a prerequisite to allowing  |
|               | deemed feasible by | this policy to proceed."* FAA  |
|               | FAA on page 4 are  | has revised the interim policy |
|               | rapid descent      | to eliminate the need to       |
|               | systems and engine | calculate the pressure-time    |
|               | fragment           | integral. FAA has provided a   |
|               | containment        | simple table indicating the    |
|               | systems. CAA       | maximum time exposure to       |
|               | considers the      | altitudes. This approach has   |
|               | policy should also | been coordinated within the    |
|               | include a          | FAA including the office of    |
|               | statement that the | aerospace medicine.            |
|               | applicant should   |                                |
|               | make mitigations   |                                |
|               | at the individual  |                                |
|               | occupant level.    |                                |
|               | This would support |                                |
|               | the second part of |                                |
|               | the page 5         |                                |
|               | Conclusion,        |                                |
|               | paragraph (2)      |                                |
|               | statement \"The    |                                |
|               | petitioner should  |                                |
|               | provide            |                                |
|               | information about  |                                |
|               | any design         |                                |
|               | features that      |                                |
|               | provide enhanced   |                                |
|               | airplane emergency |                                |
|               | descent rates and  |                                |
|               | occupant           |                                |
|               | survivability.\"   |                                |
|               |                    |                                |
|               | \(7\) At the top   |                                |
|               | of page 4 it is    |                                |
|               | stated "The        |                                |
|               | average rate of    |                                |
|               | emergency descent  |                                |
|               | given above is     |                                |
|               | predicated on the  |                                |
|               | airplane meeting   |                                |
|               | the provisions of  |                                |
|               | 25.903(d) and that |                                |
|               | the airplane is    |                                |
|               | designed such that |                                |
|               | in an event of an  |                                |
|               | UEF the airplane   |                                |
|               | structure, systems |                                |
|               | and other          |                                |
|               | engine(s) function |                                |
|               | to enable an       |                                |
|               | emergency (i.e.,   |                                |
|               | VMO/MMO) rate of   |                                |
|               | descent." CAA      |                                |
|               | considers the      |                                |
|               | policy should      |                                |
|               | include a          |                                |
|               | statement that the |                                |
|               | applicant should   |                                |
|               | take due account   |                                |
|               | of maximum hole    |                                |
|               | size caused by     |                                |
|               | fragments,         |                                |
|               | including those    |                                |
|               | from of one-third  |                                |
|               | disc and           |                                |
|               | intermediate disc  |                                |
|               | failure            |                                |
|               | (harmonized AC/AMJ |                                |
|               | 20-128A d(2)       |                                |
|               | refers).           |                                |
|               |                    |                                |
|               | \(8\) Page 2,      |                                |
|               | Impending          |                                |
|               | Rulemaking,        |                                |
|               | rightly states     |                                |
|               | that an ARAC       |                                |
|               | working group is   |                                |
|               | considering a new  |                                |
|               | regulatory         |                                |
|               | standard and that  |                                |
|               | *\"This memorandum |                                |
|               | may be updated     |                                |
|               | based on the final |                                |
|               | ARAC               |                                |
|               | recommendation.\"* |                                |
|               | The memorandum     |                                |
|               | also, rightly,     |                                |
|               | describes some of  |                                |
|               | the fundamental    |                                |
|               | technical issues   |                                |
|               | on which there is  |                                |
|               | controversy. CAA   |                                |
|               | considers          |                                |
|               | therefore that     |                                |
|               | another statement  |                                |
|               | should be added to |                                |
|               | make Petitioners   |                                |
|               | aware that         |                                |
|               | approvals granted  |                                |
|               | from use of this   |                                |
|               | policy might be    |                                |
|               | affected or even   |                                |
|               | rescinded should   |                                |
|               | an unsafe          |                                |
|               | condition be       |                                |
|               | identified from    |                                |
|               | the MSHWG studies. |                                |
|               | Because of the     |                                |
|               | lack of            |                                |
|               | physiological data |                                |
|               | at high altitudes  |                                |
|               | we find it         |                                |
|               | difficult to       |                                |
|               | accept the         |                                |
|               | pressure-time      |                                |
|               | integral method is |                                |
|               | valid, we urge the |                                |
|               | FAA to reconsider  |                                |
|               | its position on    |                                |
|               | this. We support   |                                |
|               | FAA obtaining      |                                |
|               | additional data as |                                |
|               | a prerequisite to  |                                |
|               | allowing this      |                                |
|               | policy to proceed. |                                |
+---------------+--------------------+--------------------------------+
| **[AFA:]{     | AFA provided       | [FAA response:]{.underline}    |
| .underline}** | detailed comments  |                                |
|               | which are          | \(1\) FAA's internal review    |
|               | summarized here as | and discussion within the      |
|               | issues:            | MSHWG working group regarding  |
|               |                    | the 40,000 feet limit and 2    |
|               | \(1\) 40,000 foot  | minutes above 25,000 feet      |
|               | cabin altitude     | limit indicate that there is   |
|               | limit specified in | much debate over these         |
|               | Amendment 25-87 is | numbers. The basis for the     |
|               | generally          | 40,000 feet limit per          |
|               | recognized as      | Amendment 25-87 was a paper by |
|               | necessary to       | Dr. J. Gaume in which his      |
|               | protect public     | criteria were associated with  |
|               | safety.            | time of useful consciousness.  |
|               |                    | TUC may be appropriate for     |
|               | \(2\)              | occupants with necessary       |
|               | Pressure-time      | functions in a sudden          |
|               | integral           | decompression (i.e., cockpit   |
|               | methodology        | crew) but is not appropriate   |
|               | proposed as a      | for all occupants (i.e.,       |
|               | means of           | passengers). FAA position is   |
|               | compliance lacks   | that any such altitude limit   |
|               | sufficient support | must inherently consider the   |
|               | and evidence.      | risk of exposing occupants to  |
|               |                    | such an environment. For       |
|               | \(3\) Proposed     | example, some specialists will |
|               | interim policy is  | cite any altitude above 15,000 |
|               | bad public policy, | feet as dangerous in that an   |
|               | as it circumvents  | exposure to such a pressure    |
|               | existing           | could result in morbidity or   |
|               | regulation and     | mortality to a small sector of |
|               | significantly      | the traveling public. They     |
|               | diminishes the     | believe that the risk to       |
|               | motivation to      | occupants should be "zero."    |
|               | obtain new         | FAA's position is to base our  |
|               | research data.     | decision on risk assessment    |
|               |                    | weighing in safety and health  |
|               |                    | concerns against industry's    |
|               |                    | requirements.                  |
|               |                    |                                |
|               |                    | \(2\) FAA acknowledges the     |
|               |                    | lack of exhaustive data on     |
|               |                    | this. FAA may elect to perform |
|               |                    | this testing. However, the     |
|               |                    | completion of our internal     |
|               |                    | review indicates that the risk |
|               |                    | to the occupants of short      |
|               |                    | duration exposure to altitudes |
|               |                    | above 40,000 feet but below    |
|               |                    | 45,000 feet indicates survival |
|               |                    | for all but a small number of  |
|               |                    | occupants. Should the results  |
|               |                    | of additional research prove   |
|               |                    | that this is not the case, FAA |
|               |                    | may modify this interim policy |
|               |                    | as needed. However, it is more |
|               |                    | likely FAA would utilize such  |
|               |                    | information in the rulemaking  |
|               |                    | activity.                      |
|               |                    |                                |
|               |                    | \(3\) FAA disagrees. The       |
|               |                    | procedure outlined in the      |
|               |                    | policy memo clearly states the |
|               |                    | need for the applicant to      |
|               |                    | pursue the exemption process.  |
|               |                    | All applicants may avail       |
|               |                    | themselves of this process on  |
|               |                    | any regulation. The exemption  |
|               |                    | process does not circumvent    |
|               |                    | regulations but, rather        |
|               |                    | provides a complementary       |
|               |                    | alternative to them when an    |
|               |                    | applicant can establish that   |
|               |                    | the alternative is in the      |
|               |                    | public interest.               |
+---------------+--------------------+--------------------------------+
| **[Airbus]{   | Airbus provided    | FAA response:                  |
| .underline}** | detailed comments  |                                |
|               | which are          | \(1\) FAA accepts this change. |
|               | summarized here:   | However, FAA has revised the   |
|               |                    | interim policy and eliminated  |
|               | \(1\) In Table 1   | Table 1. FAA has provided a    |
|               | -- Descent Speed   | simple table indicating the    |
|               | versus Altitude,   | maximum time exposure to       |
|               | an average         | altitudes in lieu of the more  |
|               | emergency descent  | complex pressure-time          |
|               | speed of 7,000     | integral. It was felt that the |
|               | ft/min should be   | inclusion of Table 1 was       |
|               | 42,500 feet        | redundant.                     |
|               | instead of 42,250  |                                |
|               | in order to be in  | \(2\) FAA has received other   |
|               | line with the      | comments on this issue as well |
|               | other values.      | and has taken it into          |
|               |                    | consideration in the final     |
|               | \(2\) Request      | version. FAA believes that     |
|               | clarification on   | incorporation of the noted     |
|               | text in paragraph  | design features is at the      |
|               | below Table 1,     | discretion of the manufacturer |
|               | regarding when     | in order to ensure successful  |
|               | redundant          | compliance to the intent of    |
|               | spoiler/speed      | the requirement. The intent of |
|               | brake deployment   | mentioning these systems was   |
|               | and automatic      | to denote that there are       |
|               | descent systems    | state-of-the art design        |
|               | are required.      | features which are available   |
|               |                    | and could be incorporated into |
|               | \(3\) Noted that   | a design to enhance            |
|               | the attachment     | survivability of the           |
|               | describing the use | occupants. The issue of when   |
|               | of a transform     | they should be incorporated,   |
|               | function that is   | depends upon the specific      |
|               | not the selected   | performance characteristics of |
|               | function per the   | an airplane. The successful    |
|               | ARAC.              | applicant will incorporate     |
|               |                    | those features that ensure     |
|               |                    | even with the loss of an       |
|               |                    | engine and associated (i.e.,   |
|               |                    | engine driven) systems that    |
|               |                    | the airplane retains           |
|               |                    | sufficient descent speed       |
|               |                    | capability to enhance occupant |
|               |                    | survivability. Note that the   |
|               |                    | FAA has revised the interim    |
|               |                    | policy and the table 1 that    |
|               |                    | appeared in the draft policy   |
|               |                    | is no longer present in this   |
|               |                    | final policy.                  |
|               |                    |                                |
|               |                    | \(3\) The ARAC direction does  |
|               |                    | not limit the FAA in the       |
|               |                    | interim policy nor final       |
|               |                    | rulemaking activity. FAA       |
|               |                    | elected to use a transform     |
|               |                    | function that was more         |
|               |                    | conservative than that         |
|               |                    | proposed by the ARAC group for |
|               |                    | the approximation of the       |
|               |                    | pressure. However, FAA has     |
|               |                    | revised the interim policy to  |
|               |                    | eliminate the need to          |
|               |                    | calculate the pressure-time    |
|               |                    | integral. FAA has provided a   |
|               |                    | simple table indicating the    |
|               |                    | maximum time exposure to       |
|               |                    | altitudes. This approach has   |
|               |                    | been coordinated within the    |
|               |                    | FAA including the office of    |
|               |                    | aerospace medicine.            |
+---------------+--------------------+--------------------------------+
| **[FAA-CAMI]{ | FAA-CAMI provided  | [FAA-Transport Airplane        |
| .underline}** | detailed comments  | Directorate (TAD)              |
|               | directly to        | response:]{.underline}         |
|               | Transport Airplane |                                |
|               | Directorate (TAD)  | \(1\) The authors of           |
|               | Management which   | "Neurological Study of         |
|               | are summarized     | Simulated Decompression in     |
|               | here:              | Supersonic Transport           |
|               |                    | Aircraft," Aerospace Medicine, |
|               | \(1\) Have used    | J.B. Brierley and A. N.        |
|               | the Brierley &     | Nicholson, August 1969,        |
|               | Nicholson data     | clearly state that there were  |
|               | (Interim Policy    | no signs of permanent          |
|               | Reference 2) for   | physiological harm to any      |
|               | monkeys but        | subjects exposed to a peak     |
|               | excluded their     | chamber altitude of 42,500     |
|               | conclusions that   | feet pressure altitude. In the |
|               | "the maximum cabin | results section of this        |
|               | altitude should    | reference the authors state,   |
|               | not exceed 36,000  | "There was no evidence of      |
|               | feet, as above     | locomoter impairment in any    |
|               | this severe        | animal following the various   |
|               | disturbances in    | decompressions." In addition,  |
|               | the spontaneous    | they state that, "There was no |
|               | activity of the    | evidence of brain damage in    |
|               | brain are          | any animal." We elected not to |
|               | produced," and     | use their conclusions because  |
|               | that "maintenance  | they are predicated on the     |
|               | of pulmonary       | assumptions that the authors   |
|               | ventilation is     | used in defining their         |
|               | required for       | experiment which are functions |
|               | survival from      | of the airplane design. Some   |
|               | exposures up to    | of their assumptions were      |
|               | 42,500 feet." In a | wrong.                         |
|               | second             |                                |
|               | publication,       | TAD elected to exclude much of |
|               | Nicholson wrote    | the text from the paper for    |
|               | that the monkeys   | the sake of brevity but        |
|               | had permanent      | included the complete          |
|               | neurological       | reference so that any          |
|               | injury.            | interested reader could review |
|               |                    | the entire report. TAD was not |
|               | \(2\) Have been    | aware that one of the authors  |
|               | based on the       | recanted the stated conclusion |
|               | results of older   | in a later report. However,    |
|               | tests with         | TAD elected not to include all |
|               | animals, and have  | of the conclusions from the    |
|               | not used the       | paper because the authors made |
|               | results of more    | assumptions about airplane     |
|               | recent research    | performance and rate of        |
|               | with humans who    | decompression that are not     |
|               | were tested to the | representative of a worst case |
|               | "brink of          | decompression in the real      |
|               | physiological      | world. The rate of             |
|               | incapacitation" by | decompression (ascent of the   |
|               | Dr. Mohler (OAM    | chamber) took much longer than |
|               | Report AM 70-12,   | a rapid decompression. This    |
|               | Physiologically    | exposed the animals to a       |
|               | Tolerable          | longer duration of hypoxia     |
|               | Decompression      | than would occur in a real     |
|               | Profiles for       | airplane sudden decompression. |
|               | Supersonic         | In addition the rate of        |
|               | Transport Type     | re-pressurization (descent of  |
|               | Certification,     | the chamber) was slower than   |
|               | July 1970). Since  | many airplanes (in terms of    |
|               | their exposures    | their average rate of descent  |
|               | were limited to 2  | to 25,000 feet) are capable of |
|               | minutes at 25,000  | providing. This also increased |
|               | feet, no human     | the duration of the exposure.  |
|               | subject had        | The author's conclusions are   |
|               | permanent          | based upon their observations  |
|               | neurological       | of subjects during a           |
|               | injury. Dr. Mohler | "triangular profile." While    |
|               | also provided data | this represents the best       |
|               | on human           | available data, it is not      |
|               | accidental         | representative of a sudden     |
|               | exposures in which | decompression on a real        |
|               | the parachutist    | commercial airplane. A more    |
|               | died, and on page  | correct representation of such |
|               | 7 of AM 70-12, he  | a profile would be to say      |
|               | reproduced Boeing  | "half-a-triangular profile."   |
|               | Company Tables     | This is not trivial for it     |
|               | that were proposed | represents a significant       |
|               | to update FAR      | lessening of the duration of   |
|               | 25.841(a) and that | the exposure. The time that it |
|               | recommend the      | took the chamber to go from    |
|               | "Cabin altitude    | initial pressure to minimum    |
|               | may not exceed     | pressure was much longer than  |
|               | 37,000 feet,       | a rapid decompression of an    |
|               | assuming passenger | actual large commercial        |
|               | supplemental       | airplane. The time spent above |
|               | oxygen is          | 10,000 feet pressure altitude  |
|               | present."          | for the chamber was much       |
|               |                    | longer than an actual large    |
|               | \(3\) Have been    | commercial airplane would      |
|               | based on the       | spend. The time spent above    |
|               | erroneous          | 25,000 feet pressure altitude  |
|               | assumption that    | for the chamber was much       |
|               | the FAA believes   | longer than an actual large    |
|               | the severity of    | commercial airplane would      |
|               | the neurological   | spend. The time spent above    |
|               | injury can be      | 40,000 feet pressure altitude  |
|               | determined by the  | for the chamber was much       |
|               | pressure field and | longer than an actual large    |
|               | the duration of a  | commercial airplane would      |
|               | decompression      | spend. FAA/TAD believes that   |
|               | event. Dr.         | this makes the animal data,    |
|               | Ernsting (Interim  | conservative in that the risk  |
|               | Policy Reference   | to human beings on a large     |
|               | 3) stated that     | commercial airplane subject to |
|               | "the calculations  | a rapid loss of cabin pressure |
|               | used to develop    | would be less than if they     |
|               | the pressure-time  | were subjected to the          |
|               | integral approach  | "triangular profile" in the    |
|               | were wrong," "the  | paper.                         |
|               | assumptions were   |                                |
|               | unsound," and the  | \(2\) CAMI is correct that Dr  |
|               | tests to validate  | Mohler Chief, Aeromedical      |
|               | the pressure-time  | Applications Division,         |
|               | integral approach  | authored a FAA Aviation        |
|               | would be           | Medical Report (AM 70-12) on   |
|               | "unethical." He    | the "Physiologically Tolerable |
|               | also stated "As I  | Decompression Profiles for     |
|               | commented          | Supersonic Transport Type      |
|               | previously, there  | Certification," July 1970. In  |
|               | is no way in which | the report he cites            |
|               |                    | observations from 4            |
|               | the actual         | depressurization tests         |
|               | alveolar           | conducted at CAMI and he       |
|               | PO~2~-time profile | describes a particular test    |
|               | can be predicted   | where subjects were taken to   |
|               | with any degree of | 25,000 feet chamber altitude   |
|               | accuracy --        | for 1 minute without oxygen    |
|               | certainly not that | (page 11). TAD views this as   |
|               | would be required  | only an opinion expressed and  |
|               | to produce any     | not a conclusion. TAD notes    |
|               | valid correlation  | that some humans can climb to  |
|               | between the        | Mount Everest at 29,035 feet   |
|               | alveolar           | without oxygen. At that        |
|               | PO~2~-time         | altitude the blood saturation  |
|               | Integral and the   | level is near 30% capacity but |
|               | incidence of       | they function for an extended  |
|               | cerebral           | period of time and they        |
|               | damage/death (if   | survive. That is above the     |
|               | one exists!)." "I  | point of Dr Mohler's "brink"   |
|               | have emphasized in | comment. While the issue of    |
|               | my previous        | acclimatization certainly      |
|               | comments that      | enters into the scenario, the  |
|               | there are at       | fact is that people can and do |
|               | present no grounds | function, albeit poorly, for   |
|               | either theoretical | an extended period of time at  |
|               | or experimental to | this altitude. In addition,    |
|               | support the use of | CAMI should recall during the  |
|               | the time integral  | MSHWG activity that (a) Dr     |
|               | of the alveolar    | Mohler wrote a letter to the   |
|               | PO~2~ below 30 mm  | Boeing Company expressing his  |
|               | Hg (altitudes      | support of their challenge to  |
|               | above 25,000 feet) | the specific requirements of   |
|               | even if it could   | 25.841 during failure events   |
|               | be determined, to  | and (b) Dr Mohler (a member of |
|               | distinguish        | the MSHWG ARAC working group)  |
|               | quantitatively     | is fully supportive of this    |
|               | between exposures  | pressure-time integral         |
|               | which will produce | approach. However, FAA has     |
|               | brain damage and   | revised the interim policy to  |
|               | those which will   | eliminate the need to          |
|               | not." "I conclude  | calculate the pressure-time    |
|               | therefore that in  | integral. FAA has provided a   |
|               | the absence of     | simple table indicating the    |
|               | relevant           | maximum time exposure to       |
|               | experimental       | altitudes. This approach has   |
|               | studies and the    | been coordinated within the    |
|               | known complexities | FAA including the office of    |
|               | of the             | aerospace medicine.            |
|               | relationship in    |                                |
|               | acute hypoxia      | \(3\) As previously noted, FAA |
|               | between the time   | has revised the interim policy |
|               | course of alveolar | to eliminate the need to       |
|               | PO~2~ and the      | calculate the pressure-time    |
|               | PO~2~ in           | integral. FAA has provided a   |
|               | vulnerable areas   | simple table indicating the    |
|               | of the brain that  | maximum time exposure to       |
|               | it is not          | altitudes. This approach has   |
|               | warranted to       | been coordinated within the    |
|               | employ the         | FAA including the office of    |
|               | Alveolar PO~2~     | aerospace medicine.            |
|               | Time Integral      |                                |
|               | Method which you   |                                |
|               | have developed to  |                                |
|               | measure the        |                                |
|               | severity of        |                                |
|               | hypoxia produced   |                                |
|               | by a               |                                |
|               | decompression."    |                                |
+---------------+--------------------+--------------------------------+
|               |                    |                                |
+---------------+--------------------+--------------------------------+