Quiet Technology Aerospace (QTA) has designed an upgrade of the thrust-reverser (TR) doors for the Honeywell HTF7000 engine, which powers a number of popular business jet types. The doors answer a recurrent issue with corrosion, which can be costly to put right, and follows on from a successful program to develop a carbon graphite inner inlet barrel, of which over 400 have now been delivered.
The company received an FAA supplemental type certificate (STC) for the doors in May and received approval from Europe’s EASA in September. DGAC (France), ANAC (Brazil), and Transport Canada clearance is expected soon, along with other nations that acknowledge FAA/EASA approval. The approved model list (AML) covers the Bombardier Challenger 300/350/3500, Embraer Legacy 450/500 and Praetor 500/600, and Gulfstream G280. The Cessna Longitude is due to be added early next year.
Owing to the nature of the STC, adding a new type is a relatively quick and easy process. There is no physical difference in the TR doors between one type and another, so the certification process is largely a paper exercise, transferring the approvals to the type-specific part numbers. A physical installation conformity verification and functionality check can be performed on the ground without the need for the engine to be powered up, and the process takes roughly half a day.
QTA’s TR door upgrade tackles a problem that has dogged HTF7000 operators: jet erosion corrosion. High-velocity stream, as encountered in jetpipes, breaks down the molecular surface of the doors and leaves the aluminum liable to corrosion. The products of combustion—carbon, sulfur, and nitrogen dioxide—combine readily with water to create an acidic environment that attacks the metal, particularly when the aircraft is at rest and polluted rainwater collects.
Only a certain amount of remedial action can be undertaken before a new and expensive door replacement is required, and fitting standard new doors means that they will continue to corrode in the future. Ironically, the problem is more prevalent in newer aircraft models that feature higher-thrust engines, in which the greater temperatures and pressures accelerate the erosion process.
Drawing on its expertise in engine STCs, which began with hush kits for types such as the DC-8 airliner and Gulfstream II/III in 1986, QTA has engineered a solution that tackles the root cause of the corrosion and solves the issue permanently. The corrosion-affected parts of the door are replaced with CP-70 titanium skins that conform exactly to the original door shape and maintain the same exit area—key factors in gaining certification. Due to the flexible nature of the STC, QTA can upgrade individual doors if required, although normally customers opt for the full set of six. Once the upgrade is complete, QTA becomes the certification authority for the doors and provides full after-sale support.
Like its upgraded inlets, QTA’s TR doors are backed by $50 million product liability insurance against any issues such as aircraft grounding, although the company reports that it has never received a claim. Customer satisfaction is further enhanced by the lifetime warranty being transferrable between owners.
Work to perform the upgrade is quoted as six weeks, although as production progresses, that time is being reduced. The company has two complete sets of doors available for exchange or rental to minimize aircraft downtime during the upgrade process. It also maintains six individual doors available on an exchange basis for AOG cases.
QTA is reporting a high uptake for its TR doors, stating that it is “the best-selling STC we’ve ever done.” It has already completed seven upgrade sets. Arguably, the company’s biggest issue is upgrade capacity, and it is growing the workforce to meet demand. Production is around 24 TR door sets per year, but that is being increased by adding a second shift. As the STC holder, QTA can also license out work if required. A firm believer in maintaining parts inventory, QTA already holds a stock of titanium skins sufficient for 150 door sets.
Getting the Longitude added to the AML and increasing the production rate are the main concerns at present. However, QTA is always looking to the future and eyeing other opportunities. In terms of the HTF7000 door replacement, it is talking to airframers about getting its TR doors available for new-build aircraft. The upgrade could be applied as part of the pre-delivery completion process.