2013-24727. Special Conditions: Learjet Model 35, 35A, 36, and 36A Airplanes; Rechargeable Lithium-Ion Batteries and Battery Systems

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed special conditions.

SUMMARY:

This action proposes special conditions for the Learjet Model 35, 35A, 36, and 36A airplanes. These airplanes, as modified by Peregrine, 13000 E. Control Tower Road, Unit K-4, Englewood, CO, 80112, will have a novel or unusual design feature associated with rechargeable lithium-ion batteries and battery systems. These batteries have certain failure, operational, and maintenance characteristics that differ significantly from those of the nickel-cadmium and lead-acid rechargeable batteries currently approved for installation on large transport-category airplanes. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for this design feature. These proposed special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.

DATES:

Send your comments on or before November 12, 2013.

ADDRESSES:

Send comments, identified by docket number FAA-2013-0763, using any of the following methods:

• Federal eRegulations Portal: Go to http://www.regulations.gov/​ and follow the online instructions for sending your comments electronically.
• Mail: Send comments to Docket Operations, M-30, U.S. Department of Transportation (DOT), 1200 New Jersey Avenue SE., Room W12-140, West Building Ground Floor, Washington, DC, 20590-0001.
• Hand Delivery or Courier: Take comments to Docket Operations in Room W12-140 of the West Building Ground Floor at 1200 New Jersey Avenue SE., Washington, DC, between 8 a.m. and 5 p.m., Monday through Friday, except federal holidays.
• Fax: Fax comments to Docket Operations at 202-493-2251.

Privacy: The FAA will post all comments it receives, without change, to http://www.regulations.gov/​,, including any personal information the commenter provides. Using the search function of the docket Web site, anyone can find and read the electronic form of all comments received into any FAA docket, including the name of the individual sending the comment (or signing the comment for an association, business, labor union, etc.). DOT's complete Privacy Act Statement can be found in the Federal Register published on April 11, 2000 (65 FR 19477-19478), as well as at http://DocketsInfo.dot.gov/​.

Docket: Background documents or comments received may be read at http://www.regulations.gov/​ at any time. Follow the online instructions for accessing the docket or go to the Docket Operations in Room W12-140 of the West Building Ground Floor at 1200 New Jersey Avenue SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except federal holidays.

FOR FURTHER INFORMATION CONTACT:

Nazih Khaouly, FAA, Airplane and Flight Crew Interface Branch, ANM-111, Transport Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue SW., Renton, Washington, 98057-3356; telephone [phone]; facsimile 425-227-1149.

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite interested people to take part in this rulemaking by sending written comments, data, or views. The most helpful comments reference a specific portion of the special conditions, explain the reason for any recommended change, and include supporting data.

We will consider all comments we receive on or before the closing date for comments. We may change these special conditions based on the comments we receive.

Background

On June 29, 2012, Peregrine applied for a supplemental type certificate for installing equipment that uses rechargeable lithium-ion battery systems in Learjet Model 35, 35A, 36, and 36A airplanes. The Learjet Model 35, 35A, 36, and 36A airplanes are small transport-category airplanes powered by two turbojet engines, with maximum takeoff weights of up to 18,000 pounds. These airplanes operate with a two-pilot crew and can seat up to eight passengers. The Learjet Model 35, 35A, 36, and 36A airplanes are powered by two Garrett TF731-2-2B engines, and are equipped with an emergency power supply and software-configurable avionics.

Existing airworthiness regulations did not anticipate the use of lithium-ion batteries and battery systems on aircraft. Lithium-ion batteries and battery systems have new hazards that were not contemplated when the existing regulations were issued. In Title 14, Code of Federal Regulations (14 CFR) 25.1353, the FAA provided an airworthiness standard for lead-acid batteries and nickel-cadmium batteries. These special conditions provide an equivalent level of safety as that of the existing regulation. The current regulations are not adequate for rechargeable lithium-battery and battery system installations. Additional lithium-battery and battery system special conditions are required to ensure the same level of safety as set forth by the existing regulation intended for other battery technology.

Type Certification Basis

Under the provisions of 14 CFR 21.17, Peregrine must show that the Learjet Model 35, 35A, 36, and 36A airplanes, as changed, continue to meet the applicable provisions of the regulations incorporated by reference in Type Certificate No. A10CE or the applicable regulations in effect on the date of application for the change. The regulations incorporated by reference in the type certificate are commonly referred to as the “original type certification basis.” The regulations incorporated by reference in Type Certificate No. A10CE are as follows:

Title 14, Code of Federal Regulations part 25, effective February 1, 1965, as amended by Amendments 25-1, 25-2, 25-4, 25-7, 25-18, and § 25.571(d) of Amendment 25-10; Special Conditions set forth in FAA letter to Learjet dated March 1, 1967; Special Conditions No. 25-50-CE-6 dated April 18, 1973, and Amendment 1 dated September 18, 1973. The certification basis for Models 35A and 36A also includes Special Conditions No. 25-72-CE-8 dated November 3, 1976, and Amendment 1 dated March 14, 1978. The certification basis for Model 35A, in addition to the basis listed above, includes Special Conditions 25-ANM-28 dated May 3, 1989. In addition, the certification basis includes certain later amended sections of the applicable part 25 regulations that are not relevant to these special conditions.

If the regulations incorporated by reference do not provide adequate standards regarding the change, the applicant must comply with certain regulations in effect on the date of application for the change.

If the Administrator finds that the applicable airworthiness regulations (i.e., 14 CFR part 25) do not contain adequate or appropriate safety standards for the Learjet Model 35, 35A, 36, and 36A airplanes because of a novel or unusual design feature, special conditions are prescribed under the provisions of § 21.16.

Special conditions are initially applicable to the model for which they are issued. Should the applicant apply for a supplemental type certificate to modify any other model included on the same type certificate, to incorporate the same or similar novel or unusual design feature, the special conditions would also apply to the other model under § 21.101.

In addition to the applicable airworthiness regulations and special conditions, the Learjet Model 35, 35A, 36, and 36A airplanes must comply with the fuel-vent and exhaust-emission requirements of 14 CFR part 34, and the noise-certification requirements of 14 CFR part 36.

The FAA issues special conditions, as defined in 14 CFR 11.19, in accordance with § 11.38, and they become part of the type-certification basis under § 21.101.

Novel or Unusual Design Features

The Learjet Model 35, 35A, 36, and 36A airplanes will incorporate the following novel or unusual design features: a Mid-Continent MD835-5 Emergency Power Supply that uses a rechargeable lithium-ion battery and battery system. Lithium-ion batteries and battery systems have certain failure, operational, and maintenance characteristics that differ significantly from those of the nickel-cadmium and lead-acid rechargeable batteries. Rechargeable lithium-ion batteries and battery systems are considered to be a novel or unusual design feature in transport-category airplanes, with respect to the requirements in 14 CFR 25.1353.

Discussion

The current regulations governing installation of batteries in large transport-category airplanes were derived from Civil Air Regulations (CAR) part 4b.625(d) as part of the re-codification of CAR 4b that established 14 CFR part 25 in February 1965. The new battery requirements, § 25.1353(c)(1) through (c)(4), basically reworded the CAR requirements.

Increased use of nickel-cadmium batteries in small airplanes resulted in increased incidents of battery fires and failures which led to additional rulemaking affecting large transport-category airplanes as well as small airplanes. On September 1, 1977 and March 1, 1978, the FAA issued § 25.1353(c)(5) and (c)(6), respectively, governing nickel-cadmium battery installations on large transport-category airplanes.

The proposed use of lithium-ion batteries and battery systems for equipment and systems on the Learjet Model 35, 35A, 36, and 36A airplanes has prompted the FAA to review the adequacy of these existing regulations. Our review indicates that the existing regulations do not adequately address several failure, operational, and maintenance characteristics of lithium-ion batteries and battery systems that could affect the safety and reliability of the MD835-5 Emergency Power Supply installations.

At present, commercial aviation has limited experience with use of rechargeable lithium-ion batteries and battery systems in applications involving commercial aviation. However, other users of this technology, ranging from wireless telephone manufacturers to the electric-vehicle industry, have noted potential hazards with lithium-ion batteries and battery systems. These problems include overcharging, over-discharging, and flammability of cell components.

1. Overcharging

In general, lithium-ion batteries and battery systems are significantly more susceptible to internal failures that can result in self-sustaining increases in temperature and pressure (i.e., thermal runaway) than their nickel-cadmium or lead-acid counterparts. This condition is especially true for overcharging, which causes heating and destabilization of the components of the cell, leading to the formation (by plating) of highly unstable metallic lithium. The metallic lithium can ignite, resulting in a self-sustaining fire or explosion. Finally, the severity of thermal runaway, due to overcharging, increases with increasing battery capacity due to the higher amount of electrolyte in large batteries.

2. Over-Discharging

Discharge of some types of lithium-ion batteries and battery systems, beyond a certain voltage (typically 2.4 volts), can cause corrosion of the electrodes of the cell, resulting in loss of battery capacity that cannot be reversed by recharging. This loss of capacity may not be detected by the simple voltage measurements commonly available to flightcrews as a means of checking battery status—a problem shared with nickel-cadmium batteries.

3. Flammability of Cell Components

Unlike nickel-cadmium and lead-acid batteries, some types of lithium-ion batteries and battery systems use liquid electrolytes that are flammable. The electrolyte can serve as a source of fuel for an external fire, if there is a breach of the battery container.

The problems lithium-ion battery and battery-system users experience raise concern about the use of these batteries in commercial aviation. The intent of the proposed special conditions is to establish appropriate airworthiness standards for lithium-ion battery installations in the Learjet Model 35, 35A, 36, and 36A airplanes and to ensure, as required by §§ 25.1309 and 25.601, that these lithium-ion batteries and battery systems are not hazardous or unreliable. To address these concerns, these special conditions adopt the following requirements:

• Those sections of 14 CFR 25.1353 that are applicable to lithium ion batteries.
• The flammable fluid fire protection requirements of 14 CFR 25.863. In the past, this rule was not applied to batteries of transport category airplanes, since the electrolytes used in lead-acid and nickel-cadmium batteries are not flammable.
• New requirements to address the hazards of overcharging and over-discharging that are unique to lithium ion batteries.
• New maintenance requirements to ensure that batteries used as spares are maintained in an appropriate state of charge.

These special conditions are similar to lithium-ion batteries and battery systems special conditions adopted for numerous other aircraft, including Boeing Model 787 (72FR57842; October 11, 2007).

Applicability

As discussed above, these special conditions are applicable to the Learjet Model 35, 35A, 36, and 36A airplanes. Should Peregrine apply at a later date for a supplemental type certificate to modify any other model included on Type Certificate No. A10CE, to incorporate the same novel or unusual design feature, the special conditions would apply to that model as well.

Conclusion

This action affects only certain novel or unusual design features on one model of airplanes. It is not a rule of general applicability and it affects only the applicant who applied to the FAA for approval of these features on the airplane.

List of Subjects in 14 CFR Part 25

• Aircraft
• Aviation safety
• Reporting and recordkeeping requirements

The authority citation for these special conditions is as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

The Proposed Special Conditions

Accordingly, the Federal Aviation Administration (FAA) proposes the following special conditions as part of the type certification basis for the Learjet Model 35, 35A, 36, and 36A airplanes modified by Peregrine.

These proposed special conditions require that (1) all characteristics of the rechargeable lithium-ion batteries and battery systems, and their installation, that could affect safe operation of the Learjet Model 35, 35A, 36, and 36A airplanes, are addressed, and (2) appropriate Instructions for Continued Airworthiness, which include maintenance requirements, are established to ensure the availability of electrical power, when needed, from the batteries.

The FAA proposes that the following special conditions apply to all rechargeable lithium-ion batteries and battery systems on Learjet Model 35, 35A, 36, and 36A airplanes, in lieu of the requirements of § 25.1353(b)(1) through (b)(4) at Amendment 25-113:

Rechargeable lithium-ion batteries and battery systems on Learjet Model 35, 35A, 36, and 36A airplanes must be designed and installed as follows:

1. Safe cell temperatures and pressures must be maintained during any foreseeable charging or discharging condition, and during any failure of the charging or battery monitoring system not shown to be extremely remote. The rechargeable lithium-ion batteries and battery systems must preclude explosion in the event of those failures.

2. Design of the rechargeable lithium-ion batteries and battery systems must preclude the occurrence of self-sustaining, uncontrolled increases in temperature or pressure.

3. No explosive or toxic gases emitted by any rechargeable lithium-ion batteries and battery systems in normal operation, or as the result of any failure of the battery charging system, monitoring system, or battery installation that is not shown to be extremely remote, may accumulate in hazardous quantities within the airplane.

4. Installations of rechargeable lithium-ion batteries and battery systems must meet the requirements of § 25.863(a) through (d).

5. No corrosive fluids or gases that may escape from any lithium-ion batteries and battery systems may damage surrounding structure or any adjacent systems, equipment, or electrical wiring of the airplane in such a way as to cause a major or more severe failure condition, in accordance with § 25.1309(b) and applicable regulatory guidance.

6. Each lithium-ion battery and battery system must have provisions to prevent any hazardous effect on structure or essential systems caused by the maximum amount of heat the battery can generate during a short circuit of the battery or of its individual cells.

7. Rechargeable lithium-ion batteries and battery systems must have a system to automatically control the charging rate of the battery, so as to prevent battery overheating or overcharging, and:

i. A battery-temperature sensing and over-temperature warning system with a means for automatically disconnecting the battery from its charging source in the event of an over-temperature condition, or,

ii. A battery-failure sensing and warning system with a means for automatically disconnecting the battery from its charging source in the event of battery failure.

8. Any rechargeable lithium-ion batteries and battery systems, the function of which are required for safe operation of the airplane, must incorporate a monitoring and warning feature that will provide an indication to the appropriate flight crewmembers whenever the state-of-charge of the batteries has fallen below levels considered acceptable for dispatch of the airplane.

9. The Instructions for Continued Airworthiness required by § 25.1529 must contain maintenance requirements to assure that the lithium-ion batteries are sufficiently charged at appropriate intervals specified by the battery manufacturer and the equipment manufacturer of the rechargeable lithium-ion battery or rechargeable lithium-ion battery system. This is required to ensure that rechargeable lithium-ion batteries and battery systems will not degrade below specified ampere-hour levels sufficient to power the aircraft system, for intended applications. The Instructions for Continued Airworthiness must also contain procedures for the maintenance of batteries in spares storage to prevent the replacement of batteries with batteries that have experienced degraded charge-retention ability or other damage due to prolonged storage at a low state of charge. Replacement batteries must be of the same manufacturer and part number as approved by the FAA. Precautions should be included in the Instructions for Continued Airworthiness maintenance instructions to prevent mishandling of the rechargeable lithium-ion batteries and battery systems, which could result in short-circuit or other unintentional impact damage caused by dropping or other destructive means.

Note 1:

The term “sufficiently charged”' means that the battery will retain enough of a charge, expressed in ampere-hours, to ensure that the battery cells will not be damaged. A battery cell may be damaged by lowering the charge below a point where the battery experiences a reduction in the ability to charge and retain a full charge. This reduction would be greater than the reduction that may result from normal operational degradation.

Note 2:

These special conditions are not intended to replace § 25.1353(b) at Amendment 25-113 in the certification basis for Learjet Model 35, 35A, 36, and 36A airplanes. These special conditions apply only to rechargeable lithium-ion batteries and battery systems and their installations. The requirements of § 25.1353(b) at Amendment 25-113 remain in effect for batteries and battery installations on Learjet Model 35, 35A, 36, and 36A airplanes that do not use rechargeable lithium-ion batteries.

Issued in Renton, Washington, on September 19, 2013.

Ross Landes,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.