Since aircraft ground deicing fluids are stored before use and/or submitted to dry/high humidity environments, AMS1424 and AMS1428 specifications include a number of tests to ensure the stability of the fluid.
Thermal and Hard Water Stability
This test simulates long-term heated storage without water loss before use. The test involves maintaining the fluid in a heated environment for 30 days. The pH, refractive index and viscosity of the fluid are measured before and after aging. The aged sample is tested in the WSET chamber and the results are reported. Refer to AMS1424 (3.3.2, 3.3.3) and AMS1428 (126.96.36.199, 188.8.131.52) for test details and requirements.
Foam Stability (FS)
The Foam Stability test is designed to simulate the foaming tendency of a fluid. Using a AS5901 setup, a heated fluid is sheared and poured onto test plates. After 15 minutes, the percentage of the total test area covered by foam is reported. The test procedure is in accordance with the AMS1424 specification (3.3.5).
Exposure to Dry Air (EDA)
The Exposure to Dry Air test (EDA) is designed to simulate fluid behavior following overnight exposure to dry air. In the EDA procedure, the fluid is dried out and then submitted to aerodynamic testing. The test procedure is in accordance with the AMS1428 specification (184.108.40.206).
Dry-Out by Exposure to Cold Dry Air (ECD)
The Dry-Out from Exposure to Cold Dry Air test (ECD) is designed to simulate fluid dry-out in cold air on the ramp and on the aircraft, including aerodynamically quiet areas. The fluid is poured onto aluminium plates in a controlled humidity environment. At the end of the test, the appearance of the fluid is reported. ECD procedure is in accordance with AMS1428 (220.127.116.11).
Successive Dry-Out and Rehydration Test (SDR)
The Successive Dry-Out and Rehydration test (SDR) is designed to simulate the formation of dried residues and for such to form gels upon rehydration. SDR tests involve an aluminium test plate immersed in the candidate fluid and then vertically hung in a ventilated oven in order to completely dry-out the plate. The plate is then immersed in ASTM D1193 Type IV water. At the end of the test, the weight of the rehydrated residue is determined and reported. SDR procedures and requirements are detailed in Appendix A of AMS1428 specification (18.104.22.168).
Thin-Film Thermal Stability (TFS)
The Thin-Film Thermal Stability test (TFS) is designed to simulate heated leading edge dry-out to demonstrate that a dried-out fluid does not have undesirable texture/qualities. Such a dried-out fluid will not provide holdover time. The fluid is poured onto a bare aluminium test plate. The test plate is inclined at a 10° and placed in an oven for 60 minutes. The plate is then removed and allowed to cool. At the end of the test, the plate is inspected and its appearance is reported. TFS procedures and requirements are detailed in the AMS1428 specification (22.214.171.124).
Cold Storage Stability (CSS)
The Cold Storage Stability test (CSS) is designed to simulate the stability of the fluid cycling between cold temperature and room temperature. In CSS tests, the fluid is submitted to a 24 hour -20 °C/+20°C cycling for 10 days. At the end of the test the pH, refractive index and viscosity are measured and compared to original values. The CSS procedures are in accordance with AMS1428 specification (126.96.36.199).
Storage Stability (SST)
The Storage Stability Test (SST) is designed to simulate storage in tanks. The fluid is tested in accordance with ASTM F1105. SST procedures are in accordance with AMS1428 specification (188.8.131.52).