Helipad Technical Specifications
Determination of helipad size – ICAO criteria
Helipad size determination in accordance with the current ICAO SARPs is based on a number of factors, notably the helicopter greatest overall dimension (D) and the Performance Classification of the helicopter operations.
For conventional helicopters with a single main rotor, D is the overall length with the main and tail rotors turning. The ICAO SARPs assume that for elevated heliports, the FATO and TLOF are coincidental.
The following discussion refers to elevated heliports which are the principal application of the XE range of helidecks.
The size of a FATO intended to be used by helicopters operated in Performance Class 1 shall be as prescribed in the helicopter flight manual (HFM) except that, in the absence of width specifications, the width shall be not less than 1 D of the largest helicopter the FATO is intended to serve.
The size of a FATO intended to be used by helicopters operated in Performance Class 2 or 3 shall be of sufficient size and shape to contain an area within which can be drawn a circle of diameter not less than 1 D of the largest helicopter when the MTOM of helicopters the FATO is intended to serve is more than 3 175 kg or 0.83 D of the largest helicopter when the MTOM of helicopters the FATO is intended to serve is 3 175 kg or less (with a recommendation that 1 D is applied for the smaller helicopters)
The FATO is surrounded by a safety area which extends beyond the FATO by nominated distance criteria including having a minimum external dimension of 2D. A notable change introduced in the third edition of Annex 14 is that the safety area need not be solid.
As an example of the application of the criteria for a Sikorsky S76 operating in Performance Class 2, the FATO needs to be of sufficient size to accommodate a circle of 16.00m, the S76 D value. The S76 PC2 FATO would be surrounded by a safety area with an external dimension of 32metres, (2D).
The Bell 412EP has a D value of 17.1 metres and a minimum FATO size of 22.9m by 26.5m as prescribed in the flight manual for operations in Performance Class 1 from an elevated helipad with restricted adjacent drop down height. That FATO would be surrounded by a (non-solid) safety area the minimum external dimensions of which would be 34.2 meters (2D) by 35.05m (26.5m + 0.5D).
Rescue and fire fighting provisions – application of icao sarps
- ICAO provides relevant SARPS and associated guidance material in relation to the provision of RFF facilities in Annex 14 Volume II and the Heliport Manual. The ICAO provisions are essentially the same as those detailed by the UKCAA in CAP 768 and 437 as discussed above.The ICAO SARPs classify the levels of protection needed for elevated helipads by dividing them into H categories according to the size of the helipad. H1 helipads are up to 15m in diameter, H2 up to 24m and H3 from 24m to 35m. As an example, an H2 helipad will require (a) performance level B foam applied at 500lpm for 10 minutes plus (b) complementary agents which are usually hand held fire extinguishers to be situated at the helipad area.
- ICAO also cautions that ‘although the amount of fuel carried by helicopters is generally less than that carried by aeroplanes, a more serious fire situation can occur as the fuel tank is located underneath the occupied portion of the fuselage and close to the engine. In other words, burning fuel in a helicopter crash is more likely to remain within the area adjacent to the helicopter and thus the resulting fire situation may be more serious than one involving an aeroplane of similar size.’ (Heliport Manual, 1995, para 6.1.7)
- The best way to meet these requirements and to afford the maximum fire protection for helicopter crew, passengers, building occupants and third parties adjacent to the building is to install a DIFFS unit to the helipad. DIFFS is an acronym for “deck integrated fire fighting system” and consists of a water or foam source, actuators, sensors, pipes and nozzles which spray foam or water onto the helipad. The helipad itself should be of the Enhanced Safety™ type which contains a built-in, automatic fire suppression system.
- In November 2008, representatives from international organizations including the UK CAA and members of the ICAO Heliport Design Working Group attended live fire tests on the XE Enhanced Safety helideck with a DIFFS capability. The tests were organized by Aluminium Offshore and the overwhelming response from senior representative in attendance was support for the passive helideck with DIFFS option as a world best practice for helipad fire control.
- The UK CAP437 guidance material was revised in December 2008 following the demonstration of XE Enhanced Safety Deck with water based DIFFS capability. Although the current version of Annex 14 Volume II does not included reference to the benefits of helidecks with a passive fire suppression system and integrated DIFFS capability, it is anticipated that discussion of the option will be included in future revisions of the Annex and the Heliport Manual in a similar manner to the CAP437 guidance.
Rescue and fire fighting provisions – UKCAA guidance
The UK Civil Aviation Authority is a regulator that produces regulatory and advisory publications in a range of formats including the Civil Aviation Publication (CAP) series. Annex 3 to Chapter 21 of CAP 768 Guidance Material for Operators (1st edition August 2008) provides the following comments in relation to and Rescue and Fire Fighting Services (RFFS) for onshore helicopter landing sites and references the technical guidance for presented in CAP437 Offshore Helicopter Landing Areas – Guidance on Standards (6th edition, Dec 2008) which strongly encourages consideration of the use of a Deck Integrated Fire Fighting Systems (DIFFS) on elevated facilities.
7.2 Particular problems arise from the operation of helicopters at elevated heliports that require special attention with regard to the RFF provisions. One important aspect is the confined and restricted space available on the average elevated heliport. This will impose restrictions on foam monitor and/or hose positioning and general fire-fighting tactics. It is feasible that an accident could result in a fuel spill with a fire situation which could quickly cut off or reduce the already limited routes of escape to a place of safety for the helicopter occupants. In addition the accident or fire may involve RFF facilities located adjacent to the landing area. As a result the requirement for the amount of extinguishing agent at elevated heliports is based on a fire fighting action which may be required to last much longer than at surface level heliports. In addition, at an elevated heliport, RFFS should be immediately available on or in the vicinity of the landing area whilst helicopter operations are being conducted in order to achieve a rapid ‘knock-down’ response.
7.3 At an elevated heliport, at least one hose line, complete with nozzle/branch pipe and capable of delivering foam in a jet spray/aspirated pattern at 250 L/min, should be provided. It is also considered essential at an elevated heliport to be able to apply the fire-fighting agents, both principal and complementary, to the entire landing area irrespective of the wind direction. To achieve this and to overcome the possibility of a monitor being involved in the accident, it is necessary that at elevated heliports in Category H2, that at least two monitors be provided each having a capability of achieving the required discharge rate, and positioned at different locations around the helideck so as to ensure the application of foam to any part of the landing area under any weather conditions. Alternatively, a system of hand controlled branch lines or a deck integrated fire-fighting system (DIFFS) may be considered. Further technical guidance is available in Chapter 5 of CAP437; Offshore Helicopter Landing Areas – Guidance on Standards.
To further ensure the application of the agent to the entire landing area, monitors should preferably be operable from a remote control position located clear of the landing area and easily accessible.
UKCAA published CAP1264 “ Standards for Helicopter Landing Areas at Hospitals” in Feb 2016 and this keenly awaited Standard produces admirable guidance in an area with much need for this guidance. The growth of elevated hospital helipads is very rapid and this in turn leads to a need for standards which also provide guidance on how best to deal with the different situation of an elevated helipad (defined as a landing surface which is more than 3m off the ground) as compared with a ground level site.
“The safety of helicopter operations is clearly paramount to any design for an HLS at a hospital and there can be no alleviations from the regulations due to the emergency nature of an operation. In the interests of most easily assuring the optimum operating environment for helicopters, this CAP promotes the design of elevated (rooftop) heliports, as the ‘package’ most likely to deliver a safe and friendly environment for helicopters operating to a hospital landing site (HLS) in the UK. This focus is chosen because heliports located at a good height above ground level, usually at rooftop level, tend to provide the best long-term operating environment for helicopters, by raising the landing area up above obstacles which might otherwise compromise flight operations. An elevated heliport, in addition to delivering the best safety outcomes for the helicopter and facilitating the complex needs of a critically ill patient, also has the best potential to deliver more effectively on environment performance, by reducing the incidence of helicopter noise and downwash at surface level, and delivering a more secure HLS – by creating a landing site that is securely protected from inadvertent or deliberate entry by members of the public.”
CAP1264 has the same introduction to fire safety as CAP768 in outlining the difficulty of fire fighting in an elevated space and the limited escape routes available.
It is foreseeable that an accident could result in a fuel spill with a fire situation which could quickly cut off or reduce the already limited routes of escape to a place of safety for the helicopter occupants. The purpose for providing integrated fire-fighting services (FFS) at an elevated heliport is to rapidly suppress any fire that occurs within the confines of the heliport to allow occupants of a helicopter to evacuate to safety and, when appropriate, to protect personnel in the building beneath the heliport from the effects of a helicopter fire situation. (underlining by Aluminium Offshore)
5.4 Local fire and rescue authorities should be consulted at the earliest stages of the planning and provision of an elevated heliport to ensure that proper consideration is given to the effect that an accident could have on the structure below which the heliport is located. An aviation-related fire and/or fuel spillage poses a risk to the structure below the heliport, which if a building, may have consequences for fire and for the means of escape both from the heliport and from within the building. To protect the occupants of the building, the fire and rescue authorities may require provisions in addition to the requirements set out in this chapter, provided for initial suppression and control of a fire on the heliport. “
CAP1264, similarly with CAP437, allows helipads fitted with an Enhanced Safety (passive fire suppression system) to dispense water in lieu of foam for the fixed fire-fighting system:
“Where a DIFFS is used in tandem with a passive fire-retarding system, consisting in a perforated/ grated surface, which, in the event of a fuel spill from a ruptured aircraft tank, is capable of removing significant quantities of unburned fuel from the surface of the heliport, a water-only DIFFS to deal with any residual fuel burn may be considered “
We recommend consideration of the following practical issues when planning your elevated helipad
Size of the helipad (discussed above) and connected with the model of helicopter you intend to operate
Loading considerations — more critical for existing buildings than new structures. can the roof columns take the dynamic and static loads from the helicopter? An aluminium helipad would weigh approximately 40% of an equivalent steel helipad and about 1/8th of a concrete one. This reduces dead loads considerably on the existing building structures and could reduce the need to stiffen existing structures
Vibrations — aluminium is a much more ductile material than steel or concrete and helipads made of aluminium alloy absorb vibrations and landing loads very effectively. In most cases, if using an aluminium deck, no provision needs to be made for special shock absorbers to absorb vibrations.
Structural considerations — how will the helipad be supported? A trussed support frame may be best as this can allow reaction loads to go directly into the building columns rather than the roof.
Access and egress — we need to consider how the helipad will be accessed by normal passengers, crew and fire-fighting persons. The usual method is by two stairs situated at opposite sides of the helipad with perhaps an additional emergency stair. Continually sloping ramps are a good system for gurneys to access and exit the deck. In many hospitals, dedicated lift shafts can be provided at the foot of these ramps. These can transport the patients directly to trauma rooms.
Aesthetics — if designed together with the building, the helipad can be designed to be an aesthetically pleasing structure and very visible, rather than trying to hide it in a corner space.
Turbulence and placement of helipad — this is a complex topic and cannot be discussed at length here. However, the need for an air gap between the helipad and the building is stated: “Preferably, the helipad should be elevated such there is a clear space of at least 6ft (2m) in height between the pad and the supporting roof. This will prevent additional turbulent flow from being generated and allow more streamline flow over the helipad” (“Evaluating wind flow around buildings on heliport placement”- Federal Aviation Administration, USA, DOT/FAA/PM-84/25).
Maintenance — design for minimal maintenance. This is especially critical when the helipad is cantilevered out of the building. Again, an aluminium helipad requires virtually no maintenance.