There is no doubting the excitement amongst aviation enthusiasts and passengers about the return of ultra-long haul flights. Next generation efficient aircraft such as the Boeing 787 Dreamliner and Airbus A350 XWB have faster cruising speeds which, combined with the efficient use of fuel, make possible more point-to-point direct flights over longer distances than ever before. Alongside the cost-effective move to two engines as opposed to four and other continued innovations in engines and airframes, these new technologies are enabling airlines to set new records for non-stop flights.
Last September saw Singapore Airlines take delivery of the very first Airbus A350-900 ULR. The new ultra-long-range model, a twin-engine aircraft that can fly for up to 20 hours nonstop, has been touted by Airbus CEO Tom Enders as the beginning of a “new chapter in nonstop air travel”. On Oct. 11, it was with this model that Singapore Airlines launched its nonstop flight from Changi International Airport, Singapore, to Newark Liberty International Airport, New York. With a duration of around 18 hours and 45 minutes, and travelling approximately 16,700 km, this set the new record for the longest nonstop passenger flight in the world.
Behind the deserved fanfare and excitement amongst passengers, however, what is little discussed is the impact on a plane’s engine. This requires maintenance considerations for airlines as fleets cope with the demands of the return of ultra-long-haul flights.
Enhanced Efficiency to Fuel Ultra-long-haul Travel
The larger engines needed to power these ultra-long-haul flights have been developed to be both more fuel efficient and reliable. Fundamental improvements have been made to both the propulsive and thermal efficiency of these modern engines. Regarding the propulsive efficiency - which is the translation of hot gases into thrust - this is a key factor as the majority of the thrust for the aircraft comes from the engine’s single stage fan blades. Advances in engine design mean that more efficient thrust can be generated by fewer, lighter blades. This helps to provide propulsive efficiency while also reducing the weight of the engine. As for the thermal efficiency, this can be improved by better compression of air allied with the optimum dispersal and combustion of the jet fuel. The hot gas that is produced from the combustion can then be used more efficiently by the modern 3-D turbine design.
However, in spite of these advancements, ultra-long-haul travel inevitably creates higher temperatures in engines, which can have a significant impact from a maintenance perspective. One consequence is that the higher engine temperatures can increase the temperature of the turbine engine oil (TEO) being used which can lead to unwanted and costly carbon deposits in the engine – a process otherwise known as coking. Using high thermal stability or high-performance capability oils in the engine can play a key role in helping airlines to mitigate this. Oils that are designed specifically to provide long-term thermal and oxidative stability can continue to provide engine lubrication at higher temperatures, for longer.
Solutions with the Right Engine Oil
Ultra-long-haul travel ultimately needn’t come with a high maintenance price tag. Good upkeep of the engine through using the right turbine engine oil (TEO) is a cost-effective and efficient solution to avoiding higher maintenance costs. This may be achieved simply through the improved engine lubricating protection provided by high performance capacity (HPC) and high thermal stability (HTS) turbine oils. This reduces in-service maintenance burden, which creates further costs and disruption, therefore increasing aircraft utilisation and resulting in saved costs overall across the engine’s lifetime.
By using a TEO that can handle higher temperatures, scenarios such as coking of oil feed or scavenge tubes can be reduced or avoided. For example, using AeroShell ASTO 560 (AeroShell’s HTS oil) for PT6 engines operated by a large U.S.-based Piltatus PC 12 operator can extend the time between overhaul from 3,000 to 5,500 hours when combined with other good maintenance practices; this enables an overall saving greater than $50 per engine flying hour.
The trend toward longer flights is the product of decades of manufacturing advancements to enable long-haul travel, and engine oils have likewise been adapting over this time to continue to service the engine’s needs. As engine efficiency and reliability has been improving, even with higher turbine temperatures, engine oils with better thermal stability, along with enhanced anti-coking and high load carrying ability have also been developed.
Learning from Long-haul for Short-haul Flights
The simple lesson is that choosing the right TEO can help maintain an engine’s health, regardless of the distance it is flying. Short-haul flights too face the challenge of experiencing more frequent higher engine temperatures, due to the increased number of take-offs and climbs they undergo. The use of HTS or HPC oils will help to reduce the potential for carbon deposits in these scenarios as well.
A further point to consider is that whilst all turbine engines oils need to be compliant with military or civil specifications, not all engine oils act the same once they are in the engine. One of the key differences is compatibility of the TEO with an engine’s oil seals. In a turbine engine, elastomer seals are widely used. Although they are a relatively minor component when considered against the scale of an entire commercial aircraft, seal degradation can result in oil leaking into unwanted areas. This can result in a significant additional maintenance burden for the airlines. Choosing an engine oil that is elastomer friendly is a simple way to avoid this problem, delivering cost-savings and, more importantly, helping to improve safety.
Lesson Across Aviation
The push to put ultra-long-haul flights on the market shows no signs of slowing. In the weeks since Singapore Airlines’ setting a new flight time record, Philippine Airlines has joined the trend in announcing a direct non-stop service to New York JFK from Manila – a 16-hour flight.
A proactive strategy on the part of airlines in choosing the appropriate engine oil will ensure that they are prepared to compete in this market without paying a higher price in maintenance costs to do so. Efficient ultra-long-haul travel is the next big venture for the aviation industry, and while there is much to be celebrated, airlines need to ensure that it doesn’t come with a higher maintenance bill.
Vanessa Boag is General Manager, Shell Aviation Lubricants.
