Entry and exit
A logical place to start any cockpit assessment is with the entry and exit. The aim of this part of the evaluation is to determine the ease and safety with which the crew can enter the cockpit and also exit it under both normal and emergency conditions. As always a vital consideration is the way that the aircraft is likely to be operated. For example, if operations from field sites are likely then the effect of crews having wet and muddy footwear is considered. Similarly the effect of deck motion is taken into account when evaluating a naval rotorcraft. A slip by a crew member could result in injury or possible interference with the flight controls during rotors running entries and exits which could be disastrous. The security of the cockpit door when opened and the ease of controlling the rate of closure in high winds are also checked. When presenting the results of these tests the actions the pilot took when entering and exiting his or her station are described in some detail; photographs are often the best supporting data.
Exiting the cockpit in an emergency can literally be a matter of life and death to operational crews and therefore a thorough assessment is made in this area. From a normal seated position with the safety harness locked a simulated egress is made and timed. Any difficulty with operating the jettison control or any danger of becoming snagged on items in the cockpit is recorded. It should be remembered that following an accident the fuselage may come to rest on its side or roof and egress under these conditions is considered. For example, if a large, side-by-side seat aircraft comes to rest on its side, the crew member in the lower position may have difficulty reaching an available exit. In the case of ditching it is important that a handhold is provided at the exit to allow the pilot to remain orientated without visual cues. The force required to operate jettison controls is measured using spring balances; these forces should be light enough to allow easy operation under all conditions, even under water for example. It is essential that all controls can be operated with a single hand. Emergency ingress facilities should also be provided so that ground personnel are able to gain access to the cockpit in order to rescue an injured crew member. In a utility helicopter the safety of the passengers must not be forgotten and due consideration is given to entry and exit from the cabin.
7.2.2 Field of view
Documenting and assessing the field of view (FOV) available from the pilot’s station is an integral part of a full cockpit assessment. The FOV is measured from the aircraft design eye position (DEP) which is the point in space where the manufacturer expected the pilot’s eyes to be. The manufacturer will have designed the entire cockpit around this point so that the pilot should be able to see all the necessary items in the cockpit as well as having the best possible view of external references. Where a DEP is not available another point, known as the reference eye position (REP), is nominated from which all measurements are made. This will be the point where the assessing pilot’s eyes are with the seat adjusted to his or her normal position for flight.
Measuring the FOV involves measuring the angular position of obstructions from the DEP or REP in both azimuth and elevation and then recording this information on a chart. As each measurement is added to the chart a picture of the obstructions to the pilot’s FOV is built up. There are two main ways of presenting the FOV. The first type, shown in Fig. 7.2, employs an approximation to the Mollweide projection [7.1] and is the most commonly used presentation as it contains all the measurements made during the test and can show exactly which cockpit items are causing obstructions. It also has the advantage that the total area of obstruction can be seen at a glance. This type of presentation does have the disadvantage that it can be difficult to interpret, especially for people who do not have experience of using such charts. The second type of presentation uses a photograph using a fish-eye lens taken from the REP or DEP. The first stage when conducting the assessment is to determine the REP if a DEP is not available. For this the pilot sits in the seat which has been adjusted to his or her normal flight position. Then a marker is hung from the roof or canopy such that it is positioned between the pilot’s eyes. A minimum of three, ideally othogonal, measurements are made from fixed parts of the cockpit structure to the REP to define the point for recording in a report. A mark is then made on the forward transparency, parallel to the fore and aft axis of the aircraft and in line with the REP. This mark is used as the zero degree of azimuth point. From the REP marker, the angles to obstructions in both azimuth and elevation are measured using an inclinometer and a protractor.
Measuring the FOV on the ground provides quantitative data to support the test pilot’s qualitative opinion of the FOV during role manoeuvres: it is this latter part of the assessment process that is the more important of the two. The UK Defence Standard 00-970 [7.2] contains guidance on the minimum standards. It is extremely rare that a test programme includes dedicated flights purely to assess the FOV, therefore the test pilot has to evaluate this aspect during all test flights.
The aircraft designer faces a dilemma when planning the cockpit as he or she needs to accommodate all the controls, displays, sights, etc., but in addition must provide the pilot with the best possible view in each direction. It is worth remembering that unlike conventional aeroplanes, helicopters are not restricted to keeping the flight path close to the longitudinal axis of the aircraft and this increases the importance of having a good all-round FOV. A poor FOV can have a major influence on the operational pilot when conducting role tasks, as it will affect every manoeuvre that he or she makes. The FOV requirements of an aircraft will in turn be dependent on the role of the aircraft. For instance an attack helicopter that operates at high speed close to the ground will require a much better all-round FOV than an anti-submarine naval
helicopter. However, the naval helicopter will still require a good FOV in certain arcs to allow the pilot to judge his position and relative motion to the deck when landing on a ship. Problems with the FOV often arise when a helicopter has not been designed for the specific role in which it is used. During many mission tasks the FOV may be the factor which limits the aggression and speed with which the task can be completed.
Once the FOV of an aircraft has been assessed on its initial entry to service there is a continuing requirement to conduct re-assessments whenever the cockpit is modified. Over the life of an aircraft these cockpit modifications can be very significant and invariably they result in a deterioration of the FOV rather than an improvement. Even if the FOV does not change it is often the case that the role of the aircraft or the way in which it is employed will change requiring a re-assessment to be conducted.