Air Traffic Management for Tiltrotors

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Air Traffic Management for Tiltrotors

57TH ANNUAL CONFERENCE, Accra, Ghana, 19-23 March 2018

WP No. 98

Air Traffic Management for Tiltrotors

Presented by ANACNA

Summary

The first commercial use of tiltrotors is starting in 2018. As the performances and typical behaviour of such machines can be as similar as both airplanes and helicopters, this working paper will provide short explanation and a Questions and Answers list on how to manage tiltrotor from an ATM perspective.

Introduction

1.1. Leonardo Helicopters, formerly known as Agusta-Westland, is developing the AW609 which represents the first tiltrotor for civil use.

1.2. Tiltrotor is not a brand-new technology as they were studied since the 50’s of the 20th century. the final use has always been military. The Boeing V22 “Osprey” is the most known one and is very active in all those operations where the performances of an actual airplane (speed, load capacity, endurance) is needed in conjunction to the ones typical of helicopters (no need of landing runways, possibility to hover and to fly as slow as needed).

1.3. For certain operational scenarios, tiltrotor might be useful for civil use too. Oil platforms, offshore activity, emergency evacuation and coast patrol could benefit on the use of aircraft which can fly as fast and far as an airplane but doesn’t need long runways to take off and land.

Discussion

2.1. The regulatory framework of tiltrotors is already being developed by ICAO which is going to adopt the guidance material formulated by the Tiltrotor Sub-Group. This is expected to be published in 2018.

2.2. The Italian Air Traffic Controller Association (ANACNA) was asked to help in the development of guidance material within the Tiltrotor Sub-Group of the ICAO Flight Operation Panel (FLTOPSP).

2.3. As a result, many question raised during the studies on how ATCOs should deal with the performance and capabilities of tiltrotors which might be unknown by operators, especially if compared to helicopters.

2.4. The attachment is a joint document between Leonardo Helicopters and the Italian Air Traffic Controllers Association ANACNA which aims to provide answers to these points.

Conclusions

3.1. The Q&As is intended as informative material for the use of CAAs, ANSPs and operators on the differences between tiltrotor and conventional aircraft from an Air Traffic Management perspective. It might still be updated with the suggestions readers would provide.

3.2. For this intent ANACNA encourages to send feedbacks and suggestions to the following address: info@anacna.it

Recommendation

It is recommended that this working paper is adopted as Information Paper.

Attachment – AIR TRAFFIC MANAGEMENT FOR TILTROTORS QUESTIONS AND ANSWERS

Introduction

The history of aviation has seen many technologies developed and matured by the military prior to their introduction into commercial service such as jet propulsion, fly-by-wire flight controls and composite primary structures. Today tiltrotor technology follows a similar path, having been used successfully by the military for over 10 years in the Bell Boeing V-22, Leonardo Helicopter’s AW609 is on the verge of civil certification for commercial use.

As the speed, range, and VTOL capability of the V-22 tiltrotor has revolutionized military missions like combat search and rescue, medical evacuation, and long-range ship to shore transportation, so too will the AW609 in commercial SAR, EMS, and offshore oil and gas transportation.

The AW609’s use in civil operations will revolutionize transportation, enabling true point to point travel and help reduce congestion at busy airports.

As the technology and operational regulations are on the horizon (First commercial civil tiltrotor activity is expected in 2019), some questions, remarks or doubts might arise within the Air Traffic Management (ATM) community on how to integrate tiltrotor activities into usual aircraft management and on how to interact with tiltrotor flights. This joint document between Leonardo Helicopters and the Italian Air Traffic Controllers Association ANACNA aims to provide answers to these points.

From a Gate-to-Gate perspective this Q&A sheet is divided into the different flight phases:

1. Departure

2. In flight

3. Arrival

4. General


Airplane Mode: A configuration with the proprotors on the down-stop and set to cruise RPM.

VTOL/Conversion Mode: means all approved configurations (gated proprotor positions) and flight modes where the design operating proprotor speed is that used for hover operations.

Note: the term ”Helicopter Mode“ is not used. This is to avoid confusion as helicopter mode implies a configuration where the proprotors are fixed at 90°. This configuration is used for stable and very low speed hover only. Angles greater than 90° may be used for hovering backwards at low speed. 

Maximum Dimension: The largest overall dimension of the tiltrotor (rotors turning), equivalent to “D Value” for a conventional helicopter.


Further Guidance

In addition to this sheet, ICAO is developing guidance material for tiltrotor aircraft. It is anticipated this guidance will be issued in early 2018.

Disclaimer

This document is intended as guidance material only. The material within has the sole purpose of providing information on the differences between tiltrotor and conventional aircraft from an Air Traffic Management perspective for awareness only. The data given is based on experience from the AW609 tiltrotor, when other tiltrotors begin operating this material will require review. Whilst this material may be used to give suggestions on the way to manage tiltrotors or to provide guidance and best practice, in no way does it supersede existing national or international regulation on the affected environment and matters.

 

Q&As

1. Departure

1.1. Start-up

Q: Is there any difference in start-up time between helicopters or airplanes start-up and tiltrotors?

A: No. Start-up times are comparable with those of modern helicopters and aeroplanes.

Q: Can Tiltrotors use the same helipads as helicopters?

A: In general, yes. Advice is being sought from the ICAO Aerodromes Panel to issue guidance that tiltrotors may use helicopter helipads based on the tiltrotor’s maximum dimension.

1.2. Taxi

Q: Shall ATM expect tiltrotors to taxi on the ground or hover like a helicopter?

A: Ground taxi will be the preferred way to taxi. But a hovering taxi will be possible as well, but not recommended due to down-wash.

Q: In case of ground taxing what speed will the tiltrotor normally keep?

A: 10 kts

Q: As in some airports, runway crossing is required to be as fast as possible with written additional requirements such as mandating to have all engines on, is there the possibility to ask tiltrotors to speed up? Up to what speed?

A: 20-30 kts

Q: In airport design, might wingspan of tiltrotors be considered as consistent with airplane wingspan or is there the need to add some rotating tip effects?

A: Not when compared with medium and large aircraft.

Q: Tiltrotors propellers can be set on different positions during taxiing. Could this produce undesired or higher than actual known vortex (like those already known for helicopters)?

A: No.

Q: Is there any other different behavior during taxiing from actual aircrafts?

A: No.

1.3. Roll and Take-off

Q: Does rolling on runway for take-off take the same length as airplanes? What is a typical runway occupancy of the AW609 in time/distance?

A. Less than 15 sec./Less distance (200-300 m)

Q: Can a tiltrotor roll for take-off be considered as Short Take-Off and Landing (STOL) operation?

A: Yes.

Q: Can take-off be carried both through vertical lift from Helipad (VTOL) as horizontal (STOL) from a runway?

A: Yes but limits are placed on VTOL take-off weight. If a high weight is present a STOL may be the only possible procedure.

Q: During take-off rolling, is the vortex generated by tiltrotor consistent with its wake turbulence category or is there any additional vortex area to be considered?

A: Yes the vortex generated is consistent with its wake turbulence category.

Q: What is the minimum height for tiltrotors to set from lifted take-off to horizontal configuration? How long does the conversion take?

A: It depends on the take-off procedure used (Performance Class 1 or 2). In general, there is no need to rush to complete the conversion to aircraft mode since airspeed and climb rate achieved in airplane mode and VTOL/conversion mode overlap for a long time during a standard departure profile. Minimum height will be 15 ft during take-off Performance Class 1.


2. In Flight

2.1. Climb

Q: What is the average vertical and horizontal speed of a tiltrotor during climb?

A: In Airplane mode 160 KIAS and 1000-1500 ft/m during initial climb. In VTOL/Conversion mode 80 KIAS up to 2500 ft/m.

Q: Can ATC request an increase in the rate of climb of a tiltrotor? Up to what value?

A: Yes. It depends: 2500 ft/m

2.2. Cruise

Q: Is the vortex generated by tiltrotor consistent with its wake turbulence category?

A: Yes.

Q: What is the usual and maximum cruising altitude of tiltrotors?

A: Around 20,000 ft, max 25,000 ft.

Q: What is the usual and maximum speed of tiltrotors?

A: It depends on altitude and the specific tiltrotor model, but generally speaking Vcruise will be approximately 250 KTAS and maximum speed will be around 275 KTAS.

Q: Down to what speed can tiltrotors be requested to slow?

A: For low level cruise (up to 8000ft) a slow down to hover can be achieved. Above this altitude the tiltrotor is an airplane mode and therefore can be slowed down to the standard minimum airspeed (130 KIAS (C-12 type)).

Q: In case of such request from ATC, how long does it take for a tiltrotor to slow down from cruising speed to hovering (or to the minimum speed)?

A: It will be consistent with a helicopter.

Q: What is the maximum altitude that a tiltrotor can reach in helicopter configuration both moving and hovering?

A: 8000 ft according to gross weight.

2.3. Descent

Q: Is the Top Of Descent (TOD) and subsequent vertical speed consistent with other airplanes?

A: Yes.


3. Arrival

3.1. Approach

Q: When Instrumental Final Approach has initiated, how far from the touchdown zone of the runway should ATC expect tiltrotor to start slowing down and setting for landing configuration?

A: Before IAF an initial conversion to 50° nacelle and 140 KIAS (no later than FAF); 75° nacelle and speed less than 90 KIAS after MAP.

Q: During an instrumental approach, which is the most suitable altitude/height to brake the approach and convert to go towards the Helipad?

A: The final portion of an instrumental approach will be flown already in VTOL/conversion mode (nacelle not in horizontal position >50° nacelle/max speed 140 KIAS) therefore the approach can be flow down to standard minima and after MAP perform a final speed reduction (if not performed before) to proceed to the helipad.

Q: Is the vortex generated by tiltrotor consistent with its wake turbulence category or there’s the need for additional spacing from following traffic during the approach phase?

A: It is consistent

3.2. Landing

Q: What is the final approach speed of a tiltrotor?

A: It depends on the nacelle configuration used but it can be considered compatible with modern helicopter speeds during final approach.

Q: What is the landing speed of a tiltrotor?

A: For a landing roll around 40 Kts.

Q: Can a tiltrotor land both vertically on the helipad as horizontally on the runway?

A: Yes.

Q: What is the runway minimum occupancy time after landing?

A: No additional time to the normal time required to taxi out.


4. General

Q: According to its profile, tiltrotor might be conducted as a helicopter. Would it be feasible to allow a tiltrotor to comply to the less-restrictive requirements which are related to helicopters only (e.g. visibility minima)?

A: Yes.

Q: In general, will a tiltrotor be managed over and around airports more in a helicopter configuration or more in airplane mode?

A: VTOL/Conversion mode to be managed as a helicopter.

Q: In the intent of providing Air Traffic Service Providers and Officers with tiltrotor traffic management guidance material, please add any other suggestion, data and information you might find useful:

A: In all critical phases of flight it is comparable to a helicopter. During take-off, up to 1500 ft AGL approximately, can be handled as a helicopter. From 1500 ft AGL on departure to 1500 ft AGL before landing or Holding pattern included, can be considered as an airplane, on final as an helicopter. For fuel planning and weather minima as a helicopter. Emergency procedures will be handled as a helicopter in VTOL/conversion mode.

Last Update: October 1, 2020  

December 27, 2019   316   Jean-Francois Lepage    2018    

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