We’ve all been there – suddenly realising that the situation is changing faster than we had planned, and not in a good way – be it the car ahead suddenly braking hard or flying into rapidly deteriorating weather at low level - the ensuing physiological reaction, the ‘butt clench’, precedes instinctive (trained) reaction(s), be it braking hard, swerving, or performing an immediate low-level abort; if all else fails, bracing for impact….

As a pilot, watching the feats of flying from the crews of the Large Air Tankers (LATs) and Very Large Air Tankers (VLATs) during the recent California wild fires, I suffered quite a few sympathetic ‘clenches’! The crews are wielding large aircraft, very close to the ground, flying profiles the aircraft are simply not designed for.  

Current LAT/VLAT operations encompass a wide range of commercial aircraft types, including the BAE-146, Boeing 737, and DC-10; generally legacy designs and, excepting the 737, no longer in production. The larger aircraft generally operate in concert with spotter aircraft which can define the line of attack for the tanker, aiding accurate delivery, with associated limitations, and flightdeck procedures. Operational procedures have evolved over time, with in-cockpit video showing high levels of pilot co-ordination in manually handling the aircraft to achieve accurate drops, often with complete loss of visibility at the point of release. Terrain displays almost completely ‘red’ (conflicting terrain directly ahead), significant turbulence, lots of power changes over undulating ground, maintaining visual separation on the preceding spotter aircraft, maintaining comms with other operations in the area - these are all factors a world away from airline operations, for which the basic aircraft are designed. The evolution of LAT/VLAT procedures has undoubtedly mitigated the limitations of a legacy flightdecks designed for the far more leisurely, mostly automated, operations in air transport. While the flightdecks in current legacy aircraft are largely similar (to each other), and platform  integration of flight control and flight (path) management are limited, if we move into the most modern aircraft, the level of integration leaps, which can bring issues for Air Attack. The recent announcement by Neptune Aviation that they have selected the Airbus 319 as its next LAT to initially complement, then replace, its fleet of BAE 146 air tankers, is a case in point.  

Not a 737?

The A319 is an interesting choice for a number of reasons; the first is why not a 737? The A319 is a similar size and weight to current B737-300/700 designs employed by the likes of Coulson Aviation, so why not simply use this? The cost difference between simply acquiring a turnkey 737-based solution vs. a development programme for a brand new aircraft is considerable. At a technical level, Neptune quote a minimum retardant capacity of 4,500 gallons, so slightly more the 4,000 gallons in the 737 Fireliner, and a lot more than the 3,000 gallons for the BAE-146, and obvious benefits in efficiency of the newer airframe, including range/time on station, although these advantages seem somewhat limited on first inspection. That said, and in conversation with colleagues who have flown this smaller variant, they report a relatively agile and responsive aircraft, with excess power and precise handling at low speeds, so, at least for a civil transport, suitable for the task of aerial firefighting.

Overall, an A319-based solution seems one for a longer term modernisation plan (confirmed by Neptune in their press release) but not without technical risk, including a drop system to design from scratch and addressing the highly complex Fly-By-Wire (FBW) architecture of the Airbus – it is this latter point I will be concentrating on in this discussion.

Before getting into the particular idiosyncrasies of the Airbus, it’s worth covering a few of the important technical and operational aspects, if nothing else than to highlight some of the challenges in gathering and, importantly, managing, the User and System Requirements (URs/SRs), including prioritising in the inevitable trade space – this key activity presumably lies within Neptune’s quoted “two years of extensive research and due diligence”, so in terms of the technical aspects and business case, I will assume this critical (to the outcome) activity was robust and validated. As I mention above, given the closeness of the A319 to the 737, the numbers, to me at least, only stack up for a clean sheet design over the longer term. What I will say though, and with some experience in the modification of large aircraft, is that the support of Original Equipment Manufacturer (OEM), in this case Airbus, is critical to success. Again, referring to Neptune’s original press release, “Airbus will provide comprehensive support for the lifecycle of the A319 fleet” – I’m not entirely sure this means anything more than engineering support to in-service aircraft, but I hope, in combination with Neptune’s partner Aerotec & Concept, a Toulouse based EASA Part 21J organisation, that this includes support to the design and integration. OEM/approved airframe structural data is an invaluable starting point for major modifications, likely the largest that Aerotec have undertaken to date. Airbus themselves have done their own firefighting modifications, namely the (in size) flanking C295 and A400M aircraft, so could provide significant support if so minded. All that said, it would be rather unusual for (either of) the big OEMs to get directly involved in Supplementary Type Certificate (STC) work in support of third party projects!

Before getting to the Airbus-specific aspects of a clean-sheet fire fighting design, a closer look at the C295 and A400M reveals limited value to the design of an A319-based system. Both are military aircraft with palletised firefighting capabilities; the C-295 is an original CASA design, so zero commonality; the A400M FBW/avionic system is derived from the A380, with digital FBW and sidestick inceptors, albeit with some military capabilities facilitating low level operations, not least the flightdeck layout, but more of that later. I have written previously about the inherent capability of large military transports for low level firefighting operations, exemplified by the C-130, but the cost of buying such aircraft, particularly the A400M, would be prohibitive for non-government operators.  

Airbus FBW

Setting aside the routine aspects of performing a major STC modification of a large air transport aircraft for aerial firefighting, there are a number of Airbus-specific issues that arguably explain why there are precisely no significantly modified Airbus FBW types outside of the OEM. In particular, the highly integrated avionics, including flight protections, of the Airbus FBW types represents the most significant safety of flight capability in a modern airliner, and I say this with over 15,000 hours on Airbus aircraft. However, and there’s always a ‘but’, if we examine the components of the Airbus Flight Management System (FMS), and the functions of the Flight Management Guidance and Envelope Computers (FMGECs), bringing near carefree handling comes at a cost, especially in terms of an operational implementation the system was not designed for. Not necessarily a showstopper as we’ll see, but greater care in analysing flightdeck procedures, and their attendant URs, reveals potential pitfalls for the uninitiated, or, indeed, Boeing legacy crews. As I mention above, a through review of URs, and their relative priorities, should reveal some of the things I’ll be discussing here.

So, carefree handling? Yep, pretty much – the Airbus FBW really does protect the old, tired, transatlantic pilot, having flown through the night, when arriving into the maelstrom of the London Terminal Manoeuvring Area (TMA) – when you’re tired, the irony of ‘terminal’ and ‘manoeuvre’ is not lost! However, in my A350, in common with the A380, A340, A330 and A320 series, we have a veritable broadside of protections:

Hosted in a redundant array of Flight Control Computers (FCCs), and noting terminology varies somewhat between variants, the so-called ‘Normal’ control law provides for 3 axis control, flight envelope protection and Manoeuvre Load Alleviation (MLA). The protections are not designed as structural limit protections (so don’t pedal between full rudder deflections…) but they are designed to ensure rapid and instinctive (there’s the clench!) control inputs do not result in a bad situation becoming worse.  

So what is included in these protections? They are:

       Load Factor protection – automatically limited, limits dependant on slat/flap deployment

       Pitch Attitude protection – manages energy state

       High Angle of Attack protection – protects against stall, in manoeuvre and the presence of gusts

       High Speed protection – the aircraft automatically recovers in the event of a high speed upset.

Without getting bogged down in detail, the above list means that the aircraft will actively intervene if the pilot’s inputs approach the limits defined in the FMGECs – great for a sleepy airline pilot, but there is no ability to overstress if needed to get out of a potentially catastrophic situation – as I’ve mentioned, at the ‘clench’ the outcome can be inevitable!  

In Normal Law, handling inside the flight envelope is carefree – the pilot can employ full stick deflections up to the maximum load and the maximum roll rate of 15°/sec:  

       Load: +2.5 to +1 g clean/+2.0 to 0g with flaps extended

       Pitch: +30 to -15°

       Roll: 33° stick released/67° stick fully deflected

It’s important to note that there is no directly proportional relationship between stick input and control surface position – the stick indicates demand, and the FCCs provide the coordinated roll/yaw response, respecting the flight envelope. Above 33° AOB, if the pilot releases the stick, positive spiral stability the aircraft reverts to 33°

So what does that all mean? In essence, the pilot uses the side stick to change the flight path, then relaxes - the a nil stick input within the envelope maintains the aircraft flightpath, a very different way of flying to the near continual ‘pumping’ of a Boeing yoke and takes some effort to get used to for those hyperactive pilots! Stick inputs are truly carefree, but there is absolutely no ability to exceed the limits – potentially a good and a bad thing. In case of a ‘clench’ moment, say an impending CFIT, the ability to roll wings level, apply full back stick and full power means the absolute optimum recovery is achieved – not pulling straight into a stall is a hugely powerful advantage is this case and saves valuable feet in arresting the descent/rate.  

However, in contrast to legacy aircraft, which obviously also have similar envelope limits, there is no ability to ‘pull through’, where a possibly small exceedance might guarantee a positive outcome. Whether this is a potentially important consideration in current fire fighting ops is possibly moot – but Aerial fire fighting aircraft are subject to enhanced structural fatigue monitoring, so there will be a great deal of data regarding envelope exceedances, indicating crews’ approach (no pun) – the pressure to get close to the fire in rough terrain surely pushes the limits in recovery, especially in the inevitable poor visibility at the point of contact.  

Personally, the care free stick input, particularly when startled, and potentially at low ebb (for me, quite possibly the reason for a UAS in the first place) and likely overloaded, means I can react instinctively and immediately – after twelve hours, approaching Hong Kong airport in the presence of microburst conditions on approach springs to mind, but hooning down a Californian valley is quite another thing!

The aforementioned fatigue data and operational debriefs for the crews will undoubtedly reveal how close the limits crews routinely fly, but if there is any such trend to ‘get out of jail’, then this vital point, obvious to Airbus pilots, but perhaps hidden to experienced firefighters transitioning from older legacy aircraft, needs to be captured when looking at flightdeck procedures and operations.  

The Flightdeck – a different place

I remember a brand new crew member, first flight and joining us for the landing, describing their experience – “if you two hadn’t been talking, I would have thought you were both asleep” – unconnected sidesticks, fixed thrust levers and a highly automated modus operandi makes for a near soporific experience in routine ops! Contrast this to flightdeck video of a descending aerial drop, with flailing control yokes, both pilots with hands on the thrust levers and some quite aggressive handling as the crew fights a battle with huge momentum changes, in all axes and including power. How might this translate to the new aircraft, and, again, is it adequately captured in the procedural design elements?  

While the general low speed/low level nature of the LAT operation is a given, the potential for effective use of Autothrust is significant – I do remember many legacy air transport types featuring pretty useless automatic speed control, but as I have experienced multiple times on the line and in the simulator, the Airbus Autothrust is pretty good and remains engaged for a full TCAS RA manoeuvre (as long as the flight envelope protections don’t intervene….). For the A319 in the firefighting role, a A318-derived London City (LCY) modification to the spoilers/flaps to allow for steep approaches (up to 5.5°) springs to mind – this, plus a reliable and useful Autothrust might be a real boon in areas of significant terrain roughness.  

On the other hand, the non-linked control sticks are potentially an issue. There is no ability to ‘follow me through’ and if both pilots make inputs, the result is summed, so the net result might be ‘double or nothing’ in terms of aircraft response – again from experience, the non-handling pilot really needs to keep his hand off the stick unless taking control, and the takeover procedure needs to be very carefully implemented to avoid a ‘dual input’ callout – the time it might necessary to take control is likely to be under extreme pressure and high workload – there’s the clench again! Capturing the Subtleties

So, some very positive aspects to the choice of an A319, but also some important considerations to ensure that the significant differences between the Airbus and legacy aircraft, from where many crews will inevitably be drawn, are captured at the earliest stage – I cannot emphasise the importance of folding current/revised URs into the design and modification plan enough. Obviously at a certification level, not much can be done to make major changes the cockpit, but the process highlights assumptions and constraints that might otherwise be missed, and offering an opportunity to understand how A319 systems can influence current procedures – the flight envelope protections vs aerial drop flight path setup/control, including Autothrust and engine spool up etc, comes to mind.    

Of course, these points represent the tip of the iceberg – I’m highlighting but a few aspects of a very complicated modification programme, where tension between URs and significantly different flightdeck systems will potentially affect the implementation. There are clearly a number of other areas where the highly integrated flight deck of the A319 demands attention, not least EGPWS/TAWS/TCAS, user database(s), and, as alluded, training – if I  can get somewhat uncomfortable with my FO’s control inputs as he/she approaches the flare off a shaky manual approach, I wonder how this will translate into a steep dive training drop?  

So, at high level, the steep approach flap modification and HUDs would be high priority SRs flowing down from procedural URs. The ability to control a dive, with head up Flight Path data and some residual power means I can pull out at the bottom of the valley without a ‘clench’.

Overall, I think the Airbus FBW and carefree handling will reduce workload, but transition from legacy aircraft will require careful consideration and a well thought out training plan. As a parting thought, understanding of the system is key; ‘read the Flight mode Annunciator’, avoid a repetition of Air France 296Q…