Functional Check Flights 3/4 – Planning and preparing a Functional Check Flight

Let’s deal with the aircraft first.
The check flight crew will need to know exactly what servicing has been
carried out and which systems have been disturbed. They will also need
to know if repairs, modifications and upgrades have been applied and if
so, what impact they may have on the intended flight. Some notice of the
flight is therefore required because a visit to the hangar is essential
to get to the bottom of most of these aircraft questions. Talk to the
servicing manager and look at the log books in depth. Take care with the
“can you just come down this afternoon and carry out a quick check
flight” type of request. More has often been disturbed or worked on than
at first appears.

In the longer term develop a trustful working
relationship with the mechanics in the hangar. It is amazing what they
will tell you once that trust is established. Humour between people who
know each other tends to help a lot here. If the situation does not
encourage that, due to the use of an outstation or remote facility for
instance, try to gauge the quality of the hangar guys (and their
management) and the level of pressure they have all been working under.

If
the aircraft has been cleaned or painted, pay careful attention as
these activities can give rise to numerous “knock on” technical issues
such as pitot or AOA sensor damage. Always do a detailed walk around
before such a check flight and take time over it. There have been many
examples of jacking pads left on aircraft, masking tape covering
elevator hinges and over spring tabs, not to mention paint on static
plates and vents being blocked by FOD following deep servicing or
painting.

Remember also all those systems that may have been required to be put into the Ground Test position to allow certain ground checks to be completed prior to flight clearance. Know what they are and make sure that they are all correctly re-positioned to the flight position prior to flight. Apply the principle that if it can happen, it will happen. Your job as checker is to ensure that there is no adverse effect on the flight.

You will also need to think carefully about the
weight and Centre of Gravity (CG) for the check flight. Loading ballast
in an airline is not always the easy thing it is in the manufacturers
test world and unusual CGs are not so common for the loads specialists.
Even so, ask anyone who has been around a while in the test world and
they will all have accrued a few mis-loading incidents in their life
time. An advice would be to try to put the aircraft into a weight and
loading situation with which you feel comfortable and use it as a
standard for all subsequent similar flights.

Set up a mid CG if
possible, avoid being on the limits and do consider the effect of the
weight and CG on the expected “feel” of the controls. Expect that the
aircraft will inevitably be much lighter than the aircraft on the line.
No big problem there, but think about it and consider the speeds to be
used in relation to stall speed and Minimum Control Speed. It may be
that whilst you would normally be stall speed limited, you may now be on
or near the Minimum Control Speed in the Air (Vmca) limits. It may also
be that to fully test the fuel system a specific fuel load is needed
and this may drive the CG.

As previously said, often FCFs are seen by airline flight operations management personnel as a “chance to do some flying”. Understandable and tempting as this may be, they may well be the least able in terms of their ability to spend time researching and understanding the issues, keeping their flying skills at the right level and at being able to focus completely on the task and make the right technical judgments whilst handling the “pressure” to get the aircraft back on the line. Clearly, there are some management pilots who are “right” for the task but before selecting themselves, a totally honest review of their workload, experience and technical type knowledge needs to be carried out. The primary role of management, with regards to check flight personnel, is to select the right people, then to let them do the job and finally be supportive in a safety sense, of their sometimes difficult decisions. Checkers need to know that they will be supported by their operational boss in this regard and yes they will sometimes make mistakes too.

Having a small team of hand selected crew members who are properly prepared for the task is a better approach than trying to “be fair” and rotating the checking flights amongst all to give everyone the experience. A minimum group needs to be defined consisting of sufficient support or check engineers and pilots to manage the checking workload of the airline. They should have a nominated head who, through regular meetings with the team, reviews the schedules to be used, and ensures learning from the experience gained from each flight. He / she can also recommend to senior management how aircraft to be checked should be presented. Such a person can also act as the liaison with the aircraft manufacturers to pick their brains and ensure that the airline receives the best advice possible from the manufacturers test specialists.

We recommend a crew of three wherever possible, so perhaps one of the major challenges for many airlines is to be able to integrate a ground operations engineer, a licenced quality engineer or specialist check engineer into the «test» crew environment in such a way that his voice is «heard» and his opinion weighed and valued alongside the pilot’s. No easy task in some cultures. Some airlines use a third pilot in this role but it must be clear that the primary role of this third crew member is not to be a third pilot but is to record data, maintain an over view of the checks to be carried out and most importantly to act as a safety back stop.

The checks to be undertaken will determine the number of check personnel in the full checking crew. With increasingly complex cabins and cabin systems, several Cabin Engineers are used by the manufacturers in a test capacity. The basic flight deck checking group should consist of the pilots and the senior Functional Check Engineer, who may also be cabin qualified. If needed, specialist Cabin Engineers can also be included. Take care during depressurisation checks, when using such a small team as there is a risk of one crew member being isolated in the cabin. The size of the cabin and the complexity of the systems checks in it, will generally dictate the overall size of the team in the back of the aircraft.

The airfield to be used is rarely a choice matter but it is wise to consider any implications stemming from the airfield itself. The runway capability, the height above sea level and its effect on performance, high ground and obstacles, the available navigation aids, and the active NOTAMs, all need to be considered as well as the general operational situation. For example before doing a rejected take-off or braking check, ask the question “is the operational runway the only runway in use?” and consider at what time of day the RTO will be carried out in respect to scheduled traffic. Burst a tyre at a busy time and you will not be too popular. At the bigger and busier central hubs, a short flight to another quieter airfield will probably be the answer.

ATC can be your best friend or your worst enemy in a check flight sense. The check crew have got to ensure that they are a friend. Pre-flight ATC briefings, directly between the pilots and the controller who will look after them, are very valuable and tend to act as a positive “bond” between pilot and controller. The controller will then tend to move other traffic rather than the check aircraft. No briefing and the opposite happens. The controller may become irritated by the continual and seemingly illogical demands for turns and odd levels and can then add to the workload of the check crew by making things a lot more difficult.

It is also useful to annotate the flight plan in Section 18 with the words “This flight is a check flight””. The implication to a briefed ATC controller is that it will therefore be subject to many changes of height, heading and configuration and the crew workload may be high at times.

Wherever possible a quiet ATC environment is helpful and if the ATC agency has such a quiet frequency channel, it should be used. In the pure manufacturers test environment we have dedicated controllers to ensure efficient flight separation and conflict avoidance but normally an airline does not have this privilege. However, a careful look pre- flight at the airspace and the prevailing weather can often lead to selecting a good quiet, out of the way, corner of airspace like an inactive danger area which will serve the check aircraft flight profile well. If in doubt, ask the controller for his advice and through this advice he again tacitly binds himself to the success of the mission.

Each organization will need to make a decision on the question of whether to carry out check flights by day only or by day and night. In principle, there is no major issue with carrying routine checks at night provided the meteorological conditions are VFR. However, there are nights when you can see for miles and there are other nights when it is inky black out there with no moon to assist. The combination of night and IFR should start to ring a warning bell or two and certainly will increase the workload on the crew a lot. So, it is recommended that a daylight flight is better, particularly for smaller airlines where these types of flight are flown less often and the crew currency may be lower. Also, after a significant deep service, the flight should commence in daylight if at all possible. In Airbus production testing, the last possible take off time for a first flight is related to the time of useful daylight so that at least the first slow speed handling checks can be carried out in daylight and VFR. If there are any serious weather concerns, a day only flight is the logical decision.

During certification development flight testing, the weather criteria often drive the ability to carry out a given test. However, in the check flight world it is rare to have the privilege of waiting for perfect weather. That said, it is certainly wise to know what the bottom line is for the checks to be undertaken. It may not be wise to carry out a check of the brakes in a 30 kt crosswind for example.

In Airbus, the minimum weather for a first flight of a new build aircraft is defined. If full authority flight control checks or envelope protection checks are to be done then some clear vertical airspace between clouds is needed. Autoland systems are checked out in Cat I conditions before they are used for real and a lot of attention is paid to avoid icing layers in the descent for the low speeds handling. Even small amounts of icing can significantly change the onset of buffet speeds and the schedule speeds at which warnings operate.

So as part of the flight preparation and in the cool of the office it is best to define the rules of the game that will be applied from a meteorological point of view. Apply as few rules as possible as this will allow the greatest flexibility for the check crews. Apply only as many rules as may be needed to ensure safety. But then they must be respected – always.

Bearing in mind the more normal airline “standards driven” operational situation, the check crew will need to be able to think and work «outside» the standard checklist (whilst still understanding and recognising its importance) and be comfortable doing so. Checklists should still be used but they should be used for guidance and not treated as if they are the Law. No checklist can cover all check situations.

In the airline world, Functional Check
Flights are often looked at as not being necessary at all or at best a
necessary irritation that interrupts the smooth aircraft allocation and
planning process. It means that they are often conducted under great
pressure from both operations and technical management who, of course
want to see their costly asset getting back into the schedule where it
is earning money for the airline as soon as possible. Whilst this is
absolutely understandable, especially in the smaller airlines,
management have a vital role to play in the check flight process, which
is to shield their selected check personnel from such unhelpful
pressures, whilst they in turn must do their job as safely and
professionally as possible.

Therefore,
planning for success means ensuring that the time element is
considered. Ideally check flights should be flown in daylight and
without the immediate pressure of a “back in line service” time. With
smaller airlines sometimes this is simply not possible. However, the
planning must allow time for a full briefing opportunity prior to flight
and the opportunity to fully de-brief the technical staff.

Likewise,
check flights should not be used to carry any form of passengers or
people “along for the ride” or just for “the experience”. Whilst
appearing to be tempting for various reasons, passengers in the checking
situation often lead to adding complexity, health issues and pressure
to an already complex exercise. If there is a requirement to move people
from A to B then carry out the check flight first, land and then pick
up the passengers for the subsequent transit.

Different approaches to check schedules are used. A different check schedule can be developed for each type of check flight to be carried out or a master reference check schedule can be created where certain checks are crossed through if they are not applicable. The document should not only have the item to be checked but also any associated safety warnings written before the check together with the success criteria and the maximum tolerances allowed. Where a check demands the approach towards a hard limit like a VFE limit, then the NOT BEYOND figures need to be clearly written as this will form part of the mini item briefing later in the execution phase. Avoid writing a check over two pages if possible and certainly avoid having the safety warning detached from the check to be done. Better to have gaps on the pages. Also as check flights rarely work out as planned, format the schedule to make it easy to handle and use in a different order but take care with this. Certain checks should be carried out before others i.e. low speed handling before approaches.

The Airbus In Service Aircraft Flight Test Manual (ISAFTM) can be used as a reference by Customer airlines to create their own check schedules. Along with the data provided, the other factors mentioned above should all be taken into account in the final airline version. The process, of generating one’s own check schedules, forces the discipline of thinking about all the factors mentioned and ensures a better pre-flight preparation.