According to FAA fireproofing regulations, commercial engine cowlings must be capable of withstanding a fuel-fed flame of 2000°F for fifteen minutes without flame penetration. To meet this requirement, there are two approved spray-on coatings, MA-25 S and 64-C1-2. For some time, many in the industry have been aware of reverser core failures resulting in heat induced degradation going unnoticed under spray-on coatings.
Hi-Temp Insulation provides removable reverser insulation blankets for CF6-6, CF6-50 and CF6-80 engine series. Each insulation blanket performs as a fireproof barrier in accordance with FAR 25.1191. The blanket tests were conducted in compliance with the criteria and requirements set forth in Federal Aviation Administration Advisory Circular AC 20-135. The insulation blankets prevent a burn through and/or backside ignition for a minimum of fifteen minutes.
Following is a list of the advantages removable insulation blankets offer over spray-on coatings. Many of these advantages were detailed in an article written for Aerospace Engineering by Paul Romnes, Engine Technical Services Maintenance Operations, United Airlines, San Francisco, CA.
Environmental:
- Elimination of toxic emissions during the surface preparation and spray-on application of ablative insulation coatings.
- Elimination of disposal problems associated with the coatings when removed for inspection and with the chemicals used during removal of the coatings.
- Elimination of special training and handling.
- Elimination of special purpose spray containment facilities.
Fit:
- Blankets are manufactured to tool controlled tolerances.
- Blankets are configured to pan down in specific areas to improve fit and avoid interference problems.
- Blankets are designed around areas where insulation is not required, rather than applying a coating to the entire area, reducing overall weight.
- Mechanical fasteners are used to precisely position and positively retain the blankets in place.
Consistency:
- Blankets are not affected by high vibration levels of an in-flight environment that can cause fragile coatings to disintegrate.
- Blankets are fabricated to tool-controlled dimensions.
- Blanket thickness is controlled by both quilting the insulation core and heat curing the final lay-up under vacuum.
- Blanket thermal efficiency is superior to coatings, and remains consistent due to controlled thickness and improved durability.
Durability:
- Blankets are not as easily damaged as coatings during maintenance.
- Blankets are more resistant to typical aircraft contaminants than coatings.
- Blankets do not require top coats like those used as a binder for coatings.
Maintainability:
- Blankets are easily repaired.
- Blanket repair can be done "on-wing".
- Blankets are easily removed and reinstalled for fan reverser inspections.
Inspections:
- Reverser bond lines, between the hot-side surface and the honeycomb core, can be inspected more frequently due to improved accessibility.
- With improved accessibility, a more reliable "tap test" and visual inspection can be performed.
- Reversers require less repair time since coatings are not being removed and re-applied.
Cost:
- Blankets last the life of the reverser under normal conditions.
- Maintenance costs are reduced compared to removing and re-applying coatings.
- Costly special handling, needed to use the highly toxic components of the coatings, is eliminated.
- Products related to the coatings, that have a limited shelf life and must be stored, are eliminated.
- Maintenance downtime for reverser removal and reinstallation, is reduced from ten days for coatings, to less than twelve hours for blankets.
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