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AAR S9401 Railroad Electronics Testing

AAR S9401 Railway Electronics Environmental Requirements

AAR S9401 regulatory compliance testing evaluates electronic components of railway equipment when subjected to environmental conditions. As an ISO 17025-certified environmental testing lab, we realize the importance of railway electronics equipment testing. Meeting the environmental AAR S9401 requirements can be difficult. We understand the challenges and guide companies through the process. 

Keystone provides the peace of mind that all of your needs will be met. When products do not meet the requirements, we assist with finding solutions. Our accurate test reports are delivered quickly. Our proven process helps avoid product launch delays and we provide comprehensive reports shortly after completion of the test. 

Request a quote to learn why we are one of the fastest-growing compliance test labs in the country. Contact us to receive more information on AAR S9401 regulatory compliance testing.

Summary of the AAR S9401 Railroad Electronics Test Standard

The purpose of this standard and others like it is to define performance interface requirements for railway electronics hardware and software. Note that AAR stands for Association of American Railroads. Specifically, the AAR S9401 test standard evaluates various environments in which electronic components may be in operation.

Equipment provided under these requirements must meet all performance criteria for which it is intended.

Scope of AAR Railway Electronics Test Method S9401

This standard outlines the range of environmental conditions for storage and operations of railway electronics equipment. However, the equipment needs to be designed and manufactured for use in railroad operations.

The railway electronics equipment can operate in a wide range of environments. This may range from severe to benign conditions. 

A severe environment is one in which no controls or conditioning are applied. A benign environment is one in which ambient conditions are closely monitored at a predefined level.

AAR S9401 Compliance TestingEnvironmental Testing Procedures

A description of the test parameters is specified below. The test sequence is performed sequentially on candidate railway test item(s). This is done by the same processes and the same standards as those to be procured for use in the railroad environment.

During the tests, note that certain environmental tests may weaken electronic equipment. This may then cause greater susceptibility to failure from the effects of the following environmental tests.


Railway electronic equipment must be expected to operate in altitudes ranging from -200 to 12,000 ft.


The specified storage temperatures are the lowest and highest ambient temperatures expected to be experienced by the equipment during storage or exposure to climatic extremes. The equipment is not expected to be capable of operating at these temperatures. However, the equipment must survive without damage.

The specified operating temperatures are the lowest and highest ambient temperatures expected to be experienced by equipment during normal operation. The equipment is expected to be turned on and operate within these conditions.

The test will start for 75 cycles. The extreme temperatures will be Tmax +5 °C and Tmin –5 °C. Tmax and Tmin can be found in the applicable environmental specification. Also, the temperature ramp rate of the equipment is maximized with a goal of 5 C per minute, minimum.


The equipment is humidity tested per EIA standard RS 186C. It is exposed to a relative humidity of 90-95% and a temperature of 40 C for 96 hours. The equipment must be functional and meet all test criteria before, during, and after the humidity test.


Railroad equipment is designed and manufactured to withstand specified vibrations encountered during shipping, mounting, and operation without damage. Testing can consist of any of the three methods below

Sinusoidal Vibration: This test method is performed in accordance with MIL STD-810 Method 514. The equipment must operate when subjected to the frequency range of 1 to 300 Hz. This test is applied along each of the three axes for four hours per axes.

Random Vibration: Random vibration is also performed in accordance with MIL STD-810 Method 514. The equipment is subjected to random vibration with specified power spectral density levels. Furthermore, the test is conducted along each of the three axes for a period of four hours per axes.

Mechanical Shock: The railway equipment must withstand specified shock and transient vibrations encountered in shipping and operation. The shock test is conducted per MIL-STD-810 Method 516, procedure I

Salt Fog

Exterior railway equipment must be capable of operating in heavy salt spray. This would be similar to experiences in seacoast areas and in the vicinity of salted roadways. The salt fog test is performed to the test methods in MIL-810 Method 509. The test solution is prepared as specified in ASTM B-117.


Electronic equipment must be able to prevent the penetration of rainfall at a minimum rate of 13cm/hr. Additionally, the procedure has an accompanying wind rate of 18m/sec. MIL-STD 810 Method 506, procedure I, is best suited for this test.

Electronic railroad equipment must also withstand being subjected to condensed frozen or liquid water for 20% of its life.

AAR S9401 Dust Electronic Railway Equipment TestSand and Dust

Sand and dust particles are not uncommon within the life cycle of electronic equipment on the railway. This equipment must prevent the penetration of dust that vary in size from 1 to 650μ in diameter. Electronic railroad equipment must pass when tested in the context of Test Method 510, of MIL-STD-810.

The blowing sand test procedures are required for equipment intended for use in railway electronics vehicles, wayside outdoors, and roadbed equipment categories. The blowing sand test is run for a total of 90 minutes per equipment face.


Electronic vehicle equipment must be able to resist the effects of contaminants. These may penetrate the equipment. The equipment must function in the presence of high-pressure water, any corrosives, and any of the following mentioned below without experiencing degradation in performance and reliability.

  • Iron dust
  • Oil vapor
  • Oxides of nitrogen
  • Ozone
  • Carbon dust
  • Copper dust
  • Hair
  • Loose paper
  • Common cleaning solutions


Components must be able to withstand without malfunction or damage, sunlight for 60% of their life. Sunlight is defined as a peak air temperature of 43 C, and solar radiation intensity of 1120 W/m2.

Expert AAR S9401 Regulatory Compliance Testing

Keystone has a full lab of test equipment which permits us to provide short lead times on scheduling. Our team strives to give our customers more time and energy on product development instead of testing. In addition to railroad electrical equipment testing, Keystone has a full scope of expertise including package integrity, EMC/EMI, shielding effectiveness, and IP Code testing

Contact us to receive more information on AAR S9401 environmental compliance testing.

Other applicable and referenced standards following the AAR S9401 test include the following: