The VERRES Project - VLTA Emergency Requirements Research Evacuation Study

Project VERRES (Very Large Transport Aircraft (VLTA) Emergency Requirements Research Evacuation Study) was a European Commission funded study (DG Tren: GMA2/2000/32039) under Frame Work 5 which was completed in early 2003. VLTA is a generic title for future aircraft and no specific aircraft was considered during the study. The Airbus A380 has been labelled a VLTA by some but this study was much wider in nature, including potential future designs such as blended-wing style aircraft. The project was intended to provide information to aerospace manufacturers, aviation regulators and aircraft operators specific to the issues associated with VLTA and evacuation.

There were three main work packages undertaken by the partners (FSEG University of Greenwich, Cranfield University, UK CAA, EADS, Virgin Atlantic and Sofréavia) in which the research was undertaken. While all the partners contributed to all the work packages, FSEG concentrated its main activities to Work Packages 2 and 3. The Work Packages were:

WP1 - Configurational aspects for VLTA
WP2 - Investigating the requirements of a methodology utilising analysis and partial testing
WP3 - Aspects of occupants safety for VLTA concepts
WP4 – JAA summary of VERRES activities.

WP2 - Investigating the requirements of a methodology utilising analysis and partial testing

A full copy of the WP2 report can be downloaded here. The main activities of WP2 are described below.

A Methodology and Procedure for the Introduction of Aircraft Evacuation Simulation to the Aircraft Certification Process.

As part of the research undertaken for Work Package 2, a methodology for the application of computer simulation to the certification of aircraft was suggested. While the approach is intended to address the requirements of VLTA, it is applicable to all aircraft types. The methodology suggested involves the use of computer simulation, historic certification data, component testing and full-scale certification trials. The proposed methodology sets out a protocol for how computer simulation should be undertaken in a certification environment and draws on experience from both the marine and building industries.

Along with the suggested protocol, a phased introduction of computer models to certification is suggested. Given the sceptical nature of the aviation community regarding any certification methodology change in general, this would involve as a first step the use of computer simulation in conjunction with full-scale testing. The computer model would be used to reproduce a probability distribution of likely aircraft performance under current certification conditions and in addition, several other more challenging scenarios could be developed. The combination of full-scale trial, computer simulation (and if necessary component testing) would provide better insight into the actual performance capabilities of the aircraft by generating a performance probability distribution or performance envelope rather than a single datum. Once further confidence in the technique is established, the second step would only involve computer simulation and component testing. This would only be contemplated after sufficient experience and confidence in the use of computer models have been developed.

The third step in the adoption of computer simulation for certification would involve the introduction of more realistic accident scenarios into the certification process. This would require the continued development of aircraft evacuation modelling technology to include additional behavioural features common in real accident scenarios.

Investigating VLTA Evacuation Issues using the airEXODUS Evacuation Model

A detailed study of evacuation performance using computer models being performed as part of the activities of Work Package 2. This study focused on the use of internal stairs during evacuation using computer simulation.

VLTA pose considerable challenges to designers, operators and certification authorities. Questions concerning seating arrangement, nature and design of recreational space, the number, design and location of internal staircases, the number of cabin crew required and the nature of the cabin crew emergency procedures are just some of the issues that need to be addressed. In this report we investigate issues associated with staircase design and cabin crew procedures using the airEXODUS evacuation model. A hypothetical VLTA identified as the UOGXXX, involving two decks and a passenger load of 580 passengers with a single main staircase is defined within the airEXODUS model.

The UOGXXX has nine pairs of Type A exits, four on the upper deck and five on the lower deck. This is in excess of the six exit pairs that would be required to simply cater for the number of passengers. The larger number of exits result from other regulations within CFR 25 that dictate that exits are required at each end of the cabin section and that the distance between any exit pair was not in excess of 60ft. A staircase was positioned towards the front of the aircraft so as to assist in the expeditious boarding and disembarking of passengers. Other considerations included the desire not to split a class, maintaining a three class layout and causing minimal disruption to the first class passengers. The staircase was sufficiently wide to accommodate two passengers side by side separated by a central handrail.

vrEXODUS representation of the airEXODUS simulation of evacuation from the UOGXXX using all exits.
Real Media (low quality) [11 sec] - Streamed from the server
Real Media (good quality) [0.76 MB] - downloadable

While airEXODUS has the ability to represent "extreme" passenger behaviour of the type reported in actual aviation accidents, such as seat jumping, this type of behaviour is not included in these simulations. All the cases considered here are run under certification type evacuation conditions involving:

(ii) Orderly passenger behaviour of the type found in certification evacuations,

(iii) Each exit being made ready in a representative time derived from past relevant certification tests.

All of these scenarios are simulated under 90-second certification trial conditions and are thus representative of controlled physical experiments involving real passengers. Passenger performance and behaviour on stairs is based on data gathered from marine and building environments. This assumes that the staircase design is similar to that found in buildings. A new feature of airEXODUS known as the Active Cabin Crew Management (ACCM) procedure was used in this study to simulate crew management of the evacuation process.

WP3 - Aspects of occupants safety for VLTA concepts

Trial and Data Analysis: An analysis of passenger performance on stairs and upper deck slides during evacuation trials.

A copy of the FSEG contribution to the WP3 report can be downloaded here. The main FSEG activities in WP3 are described below.

As part of the VERRES project several large-scale evacuation trials were conducted in the CRANFIELD simulator. The work of FSEG focused on the analysis of the data concerning passenger use of stairs and passenger exit hesitation time analysis for upper deck slides.

From these trials it is clear that cabin crew can exert an influence on the performance of passenger stair usage. Passenger behaviour in utilising the staircase is both rich and complex and warrants further investigation. These trials support the view that for crew to consistently make appropriate or optimal redirection command decisions that include the possibility of using the stairs as part of the evacuation route, they must have sufficient situational awareness. Equally, passengers can only make appropriate or optimal redirection decisions if they too have sufficient situational awareness. This situational awareness may need to extend between decks.


Figure 5: (a) Commencement of and (b) over-taking during DOWN stairs movement

Passengers were also noted to make heavy use of the central handrail while both descending and ascending the stairs. The presence of the central HR effectively created two staircases. By effectively separating the crowding on the stairs, reducing passenger-passenger conflicts and providing an additional means of passenger stability, it is postulated that the stair flow rates may be positively influence through the presence of the central HR. Flow rates in the UPWARDS direction was found to be greater than flow rates in the DOWNWARDS direction. This was thought to be due to the packing densities on the stairs which is a function of the motivation of the passengers, the travel speeds of the passengers and the feed and discharge characteristics of the staircase and surrounding geometry. It was also noted that the average unit flow rate in the DOWNWARDS direction was equivalent to that specified in the UK Building Regulations. Clearly, most of the parameters can be influenced by both crew procedures and cabin layout.

Concerning the passenger exit hesitation times for the higher sill height, the trials produced inconclusive results. While the exit flow rates are lower and the passenger exit delay times are longer than would be expected for a normal Type-A exit, it is clear that the extreme unassertiveness of the cabin crew positioned at the exits and the lack of motivation of the passengers exerted a strong influence on the data produced. The reaction of the passengers in these trials was to be expected as the trials were not performed under competitive conditions and the reaction of the cabin crew could also be understood as safety concerns were paramount given that these were the first trials of their type to be conducted at Cranfield.