Additive manufacturing (AM), commonly referred to as three-dimensional (3D) printing, is a modern manufacturing technology that can be applied within many different areas of the aerospace industry due to its ability to produce light and durable parts with complex geometries. Aircraft manufacturers and airlines have expressed interest in the use of AM produced parts in aircraft cabins. However, AM presents new safety challenges that must be examined, including the flammability of the 3D printed part used in the aircraft cabin. Due to the different parameters used during the production process compared to traditional manufacturing methods, it was necessary to determine the effect that variations in print parameters have on the flammability of a 3D printed part. In order to accomplish this, the following print parameters were evaluated; material type, sample thickness (number of inner layers), infill percentage, infill pattern, raster width, raster angle, and print orientation. The scope of this report only includes samples produced from the Fused Filament Fabrication (FFF) AM method, a type of extrusion-based AM process.

Testing was conducted using the Vertical Bunsen Burner (VBB) test methodology outlined in Chapter 1 of the Aircraft Materials Fire Test Handbook (FAA, 2023). In the first phase of testing, only a few variables in the samples were altered and the remaining variables were kept constant so that accurate comparisons between fire data could be made. Subsequently, a Design of Experiments (DOE) analysis was conducted to determine the interaction among multiple print variable combinations.

Results indicate that all evaluated variables had an impact on the flammability of a 3D printed part. The three variables that were observed to have the most significant effect on data were material type, sample thickness, and infill percentage. Other factors such as raster width, raster angle, print orientation, and infill pattern were observed to produce only interaction effects in conjunction with the other print variables listed.

This report summarizes a short test conducted by the Federal Aviation Administration (FAA) to determine the effectiveness of a trained canine to detect lithium batteries hidden inside of boxes. Fifteen identical cardboard boxes that either contained different types of lithium batteries, or were empty, were spread out around a building for the canine to inspect. On the initial quick scan, the dog was correct on 11 out of the 15 boxes, with more accurate results on lithium-ion batteries than lithium metal. On a second more thorough inspection, the canine was 100% accurate on all the boxes. The effectiveness of this dog in detecting lithium batteries shows that this could potentially be a reasonably accurate and practical method for future detection of non-compliant lithium battery shipments on passenger and cargo aircraft.

A study was conducted to determine the feasibility of adding the capability of measuring material smoke emissions to the Federal Aviation Administration (FAA) rate of heat release test method, which is performed in a specially developed test device that iscommonly referred to as the Heat Release Rate 2 Apparatus (HR2). A laser/sensor means of measuring cumulative smoke release, analogous to specific optical density Ds as measured in the FAA smoke emission test, was devised by using a continuous wave 670-nanometer wavelength laser and a thermopile power sensor. Tests performed in the FAA smoke emission chamber compared the output obtained from the legacy smoke chamber photometric system and the newly devised laser/sensor assembly measurement system. Neutral density light filters with varying percentage of light transmission were placed in the light paths, and specific optical density was determined for each value of percentage light transmission, which found both measurement systems to be in good agreement over the entire range of filters tested. Material smoke tests using both measurement systems wereperformed to compare the material smoke emission. In general, peak smoke-density measurements obtained with the laser/sensor system were lower than those obtained with the photometric system, though test-to-test repeatability was similar for both measurement methods. Material smoke emission tests were performed in the HR2 apparatus with the laser/sensor assembly attached horizontally such that the laser light path spanned the width of the vertical exhaust gas stream. Cumulative smoke release data obtained during the HR2 tests were affected by the conditions at the exhaust stack of the HR2. The elevated temperature at the exhaust opening was found to increase the thermopile sensor output reading; though this was compensated for by setting the sensor baseline after the HR2 has reached a stable operating temperature. In materials that produce large flames from the HR2 exhaust, thermopile sensor readings were observed to be significantly impacted, as the luminosity of the flames resulted in increased thermopile sensor output. Overall, this study demonstrated the feasibility of measuring smoke density during a heat release test in the HR2 apparatus, with mitigations employed to compensate for the elevated temperatures and possibility of visible flames at the HR2 exhaust opening.

The transport of oxidizers and compressed oxygen within aircraft is heavily regulated, largely as a result of the fatal 1996 ValuJet accident. Past Federal Aviation Administration (FAA) studies have found that released oxidizers can exacerbate burning within a halonsuppressed cargo compartment fire, potentially overwhelming the fire suppression system within an aircraft.

Recently, a request was submitted to ship medical devices containing small quantities of gaseous nitrous oxide (N2O). As part of the certification process, the manufacturer of this device completed the PHMSA-required thermal resistance and flame penetration tests; however, the packaging was unable to pass the thermal resistance portion of the required tests and small quantities of N2O were able to escape. As a result of these initial tests, the manufacturer requested an exemption from this requirement.

PHMSA requested assistance from the FAA Fire Safety Branch to determine if quantities of released N2O would significantly impact a cargo compartment fire. Although N2O is not flammable, it is an oxidizing agent that could exacerbate an otherwise controlled cargo compartment fire, and ultimately overwhelm the integrity of the suppression and containment capabilities of the system. Tests were conducted within an aircraft lower deck (LD-3) sized steel test chamber using a fire load of eighteen cardboard boxes filled with shredded paper. During each test, the shredded paper was ignited and the ensuing fire was allowed to develop. Two baseline tests were first conducted, in which the fire within the test chamber was allowed to burn unabated, without introducing N2O. Three subsequent tests were conducted in which various quantities of N2O gas (5.8 oz, 11.6 oz, and 17.4 oz) were released into the testchamber once the fire was fully developed.

Results indicated that released quantities of N2O less than or equal to 11.6 oz did not produce a significant reaction within the fire in the test chamber. However, it was observed that as the quantity of released N2O increased, more significant combustion reactions occurred. Therefore, until further data is acquired, it is recommended that the amount of N2O be limited to no more than 11.6 oz per Unit Load Device (ULD) for air transport.

A thermal event involving a package containing lithium-ion pouch cells occurred within a sorting facility of an all-cargo airline in December 2022. This package had been previously shipped via air and was being handled for delivery to its next destination. Following the incident, the package was sent to the William J. Hughes Technical Center for further evaluation using battery analysis equipment to determine the as-delivered state of charge (SOC) of the cells.

Lithium-ion cells not packed with or contained in equipment (Lithium ion batteries, UN3480) that are transported via aircraft are mandated by Federal regulations to be at a SOC no greater than 30%. Previous FAA studies have determined that lithium-ion cells exceeding this level are a serious hazard due to risk of thermal runaway and can lead to an unsafe condition on an aircraft.

Upon inspection, many of the cells in the package were observed to have significant signs of damage, including swelling and corrosion. However, it could not be determined if this damage occurred prior to or after the incident. SOC testing was performed on cells that did not show significant signs of damage. Testing determined that 14 of the 25 tested cells exceeded the maximum 30% SOC requirement. Of these 14 cells, 7 exceeded 70% SOC, with the highest evaluated cell recording a SOC of over 90%.