MS&T’s Europe Editor, Dim Jones, visited the Empire Test Pilots’ School (ETPS) at MoD Boscombe Down to track the progress of the members of the Class of 2019; by the time of this instalment, they were approaching the halfway mark, undertaking more complex and demanding tasks.

In 2003, QinetiQ and the UK MoD entered into a 25-year Long-Term Partnering Agreement (LTPA) to oversee various activities, one of which was ETPS. As time progressed, it became apparent to both the MoD and QinetiQ that ETPS could be run more cost-effectively without sacrificing the quality of the product, and a new ‘sub-LTPA’ was established in 2016 to manage the transformation of the syllabus and the fleet and to run the new course thereafter. The transformation was to be accomplished in two years, while still continuing to run the old course; this was a tall order, but the first of the new courses, the Class of 2019, commenced training on time and, on 26June this year, the new ETPS was formally opened by the outgoing Chief of the Air Staff, Air Chief Marshal Sir Stephen Hillier who, in his previous appointment as Deputy Chief of Defence Staff (Capability) had, alongside QinetiQ’s CEO, Steve Wadey, initiated the change programme.

The main ETPS course comprises fixed- and rotary-wing (FW and RW) elements, the former sub-divided into Fast-Jet (FJ) and Multi-Engine (ME) and, within each discipline, pilots and Flight Test Engineers (FTE). During my first visit, I concentrated on the FW syllabus, and flew in the Avro RJ-70 on a Pressure Error Correction Measurement exercise. This time, the emphasis was on RW – emphatically not my area of expertise, although I have had the privilege during my flying career of providing light entertainment for professional and properly qualified helicopter aircrew in a variety of rotary types.

The ETPS RW pilot syllabus is broadly the same as for FW, but with some subtle differences. UK Army, RN, RAF and international students must have a minimum of 750 hours flying experience and, these days, this will normally have been on a single operational type. The initial part of the course is a limited conversion to the ETPS types, such that the students can carry out the syllabus exercises. First, they investigate the performance characteristics in level flight (including low-speed and hover), and then in autorotation.

Next comes handling. Most modern helicopters have an Automatic Flight Control System (AFCS) which gives artificial feel; the initial investigation of basic stability and control is with the AFCS disengaged, and covers longitudinal and lateral stability in forward flight, and at low speed and in the hover. These exercises are then repeated with the AFCS engaged, before progressing to the study of High Order Flight Control Systems (HOFCS), using a specially modified variable-stability aircraft (normally a Bell 205 or 412 leased from a Canadian operator) in which, within a calculated safety envelope, the flight control ‘gains’ (the flight control response to a given stick input) and AFCS configuration can be varied by inputs from the crew, and evaluated.

The syllabus then progresses to autorotation, engine failure, engine-off landing (EOL) and the ‘Avoid Curve’. In autorotation, a helicopter is driven only by aerodynamic forces – no power from the engine. The engine is disengaged and the rotor blades are driven solely by the upward flow of air through the rotor. It is the means by which a helicopter can land safely in the event of complete engine failure. During autorotation, maintenance of the main rotor rpm (NR) is critical, since it is through converting the energy thus stored, added to that gained through forward speed, that the rate of descent can be reduced when approaching the ground, and the aircraft flared to achieve a safe landing. All but the simplest helicopters have some sort of an automatic power control system, whereby the power will be automatically adjusted to maintain NR with varying collective inputs. Autorotation performance is assessed at varying forward speeds, and also at reduced NR, which will reduce the rate of descent, but correspondingly the rotor energy available to control the final stages of the landing.

The next stage is EOL (Engine Off Landings); some students will not have much experience of this, since increasingly – as at the UK’s Defence Helicopter Flying School (DHFS) – training aircraft are now twin-engined, and some familiarization with EOL techniques will be required before progressing to the syllabus sorties. Stage 1 is the study of engine failure characteristics, and particularly the effects of varying the reaction time to a failure – also known as lever delay – on aircraft handling and performance. This leads to the formulation of the best EOL profile for the aircraft being tested and, from this, identification of the Avoid Curve – the parameters outside which, for whatever reasons, a safe EOL would be compromised. 

An International Sortie

The syllabus sortie which I followed through was the first covering autorotations, and would be flown in the single-engined Airbus H125B3e. The crew would be a Flight Test Instructor, Ian, flying in the left-hand seat (LHS), with his FT Student (Michael, from the Swiss Armed Forces) in the RHS, and an FTE student (Dave, a Royal Australian Navy officer) in the back. The sortie would be monitored in Boscombe Down’s ground telemetry station by Andy and Simon, by me and by Edgar, a RW FTE student from the Republic of Singapore. The aims of Autorotation Sortie 1 were for the students to receive instruction in test methods commonly used to evaluate helicopter autorotative performance and handling characteristics, and to receive familiarisation training on the use of telemetry. 

Ground telemetry screens at Boscombe Down, monitoring an autorotation scenario. Image credit: Dim Jones.

The H125 has two positions of the throttle twist grip on the collective lever: FLT will allow the engine control to vary the torque, thereby maintaining NR while responding to pilot performance demands; while IDLE maintains the engine at flight idle, and the collective can be used to control NR.

First, however, I was fortunate enough to get airborne in the LHS of the H125, and experience the aircraft’s handling and flight test environment. The FADEC-controlled Arriel engine gives it excellent performance, the all-round visibility is first class, and the aircraft is a delight to fly, with or without the stability augmentation system – although I am told that failure of the single hydraulic system renders the flight controls extremely heavy. The glass cockpit includes a large Flight Test Instrumentation (FTI) screen on the left-hand panel, on which can be brought up a wide variety of FTI displays; there is provision for an iPad Mini mounted on the RHS coaming, and tablets can also be mounted in front of the rear seats.

Technology does not always make life simpler, however: setting the height warning bug on the radar altimeter, which used to involve the rotation of a single knob, now requires a lengthy sequence of button-presses. My personal minder, Eric, showed me a cross-section of the 125’s capabilities, including autorotation and simulated EOL, and, under his watchful eye, I duly reprised my airborne entertainment function; alas, as always when the fun-meter is pegged in the right-hand corner, the time passed all too quickly.

The Autorotation 1 sortie comprises six serials, all starting from around 8000 ft, with a minimum height of 1000 ft above ground, save for the last serial, in which the minimum height is 500 ft agl. The first three investigate various performance parameters at the standard autorotation speed of 65 Knots Indicated Air Speed (KIAS), and target NR of 400; the acceptable range is 320-430. Serial 3 is then repeated with target airspeeds of 90 and 50 KIAS. The next two serials look at a target NR of 360 at 65 and then 90 KIAS. For each serial, the FTE, who controls the mission aspects of the sortie, records various engine and airframe parameters, such as collective position, actual NR, yaw pedal position, and rate of descent. In addition, the aircrew record any vibration encountered, using an objective numerical assessment of its severity and frequency, ranging from ‘None’ to ‘Intolerable’.

On the ground, the telemetry team monitor the sortie; their displays can be set to show the same as the airborne FTE is using, or any other set of data available from the aircraft FTI equipment. On some syllabus exercises, notably assessment of the effects of varying reaction time to an engine failure (lever delay), telemetry monitoring can be safety-critical. The final serial looks at turn performance in autorotation and, for a variety of reasons, is flown at the best-rate-of-climb speed (VY). Despite problems on startup in both aircraft and ground telemetry (Traffic Collision Avoidance System - TCAS) failure in the aircraft, comms and system issues in telemetry), the sortie progressed satisfactorily and achieved all its aims.

Formations and Tracking

Calspan's Learjet 'in-flight simulator' enables evaluations in a real flight environment that includes fully representative motion cues and real-world visual cues. Image credit: Calspan.

Meanwhile, the FW course had progressed to their HOFCS module. They had already completed sorties which explored basic flight control laws and characteristics in ‘non-augmented’ flight control systems; now they were looking at pure fly-by-wire systems, how adjustments to the control parameters can be used to modify the way the aircraft will respond to control inputs, and how to test the modified system to ensure it produces the desired results, without displaying any adverse characteristics. To this end, the HOFCS sorties are flown in the Calspan Learjet, which is essentially a flying simulator. The LHS controls are standard Learjet, the control column is a yoke, and the aircraft – when flown from the LHS – behaves as a normal Learjet. The RHS is equipped with two control stick-tops, one conventional central column-mounted and the other a sidestick. Both of these, under normal circumstances, work to a standard flight control model which produces handling characteristics similar to a Hawk. However, by use of switchery on the centre console, the crew can input variations to this standard model.

For all Calspan Learjet sorties, the LHS is occupied by a fully qualified Learjet captain, who acts as the safety pilot. The RHS is occupied by either a student Test Pilot or a student FTE. There are three sorties in the HOFCS module: one is a two-hour general handling sortie, dedicated to FTE students, and two them will share the stick time. The second is also a general handling sortie, this time dedicated to a student Test Pilot, in which he has the opportunity to experience the effects of the flight control system variations, supervised by a Flight Test Instructor in the jump-seat behind the flight deck. During the final sortie, these effects are demonstrated in the context of two exercises: close formation, simulating the ‘waiting’ position astern an air refuelling basket; and a simple guns tracking exercise, initiated from a perch position. For this sortie, the Learjet is joined by a ‘tow’ aircraft, in this case an ex-Swiss Air Force Hunter Mk58, operated by Hawker Hunter Aviation from RAF Scampton – still an iconic aircraft, not least to the many, like me, who only managed enough Hunter hours to whet the appetite, but not to satisfy it!

A Swiss-model MK58 Hunter operated by Hawker Hunter Aviation, showing the 'Sabrinas' and gunports. Image credit: Erik Bruijns.

The variables to be investigated on the sortie are: Time Delay (between control input and effect); Phase Lead; Phase Lag; and Aileron Rate Limiter. To the uninitiated, Time Delay and Phase Lag might appear to be much the same; however, I am assured that there are subtle differences. The Hunter, of course, has no AAR basket, so the visual references used to judge the formation positions are the four Aden Cannon gunports under the Hunter’s nose, and the rounded shell-case pods under the gun-pack – nicknamed ‘Sabrinas’, in honour of the eponymous actress of the 50s and 60s. The Learjet has no HUD or gunsight, so ETPS have designed an ingenious modification, using the camera function of a mobile phone fitted above the RHS forward coaming, in which a simple gunsight picture is superimposed on the camera image. Pitch control characteristics are evaluated during the approach to the ‘basket’ from astern, or while manoeuvring to track the target from the perch; roll control by laterally offsetting the aircraft to a point astern one of the Hunter’s underwing tanks and then returning to the centerline, or by placing the Hunter at the three o’clock or nine o’clock position in the ‘gunsight’ and then readjusting to the tracking picture.

The exercise involves testing each of the first three variables above for pitch and roll in each manoeuvre. The settings can be adjusted for the best results in one environment, and then carried over to the other; unsurprisingly, what’s good for guns tracking isn’t necessarily good for close formation. The plot is further complicated by the fact that no two pilots are the same, in terms of what they assess as being the optimum flight control gains; generally speaking – but not exclusively – FJ pilots tend to be ‘high-gain’ and ME pilots ‘low-gain’.

Whereas, under the right circumstances, Phase Lead and Phase Lag can enhance handling qualities, Time Lag is always bad, but an element of it may be an inescapable result of the design of an FCS. The aim is to minimise it, and then assess whether the result is acceptable or unacceptable. Phase Lead or Phase Lag, if inappropriately applied, can result in a Pilot-Induced Oscillation (PIO) which, in extreme cases, can lead to loss of control. Similarly, a rate limiter – which limits the rate at which a control response is applied, irrespective of stick input – can also induce a PIO. The results of these exercises are translated into objective assessments of Handling Qualities Ratings (HQR) and PIO susceptibility, using matrices and numerical ratings developed for that purpose. The student Test Pilot for the sortie I monitored was, once again, our Australian F/A18 pilot, Aaron. He reported that the sortie had gone well, that he had used the centre-stick rather than the side-stick throughout, and that he judged the aileron-rate-limiter function to be the most disconcerting effect, and the most likely to lead to a PIO.

Accelerated Development

When I visited, the Class of 2019 were about halfway through the course and, despite this being the first of the new syllabus and operating many new aircraft types, were less than a week behind the planned schedule. To put this in context, QinetiQ’s Director Operations Air & Space, Simon Tate, averred that “you couldn’t say that of any other [ETPS] course in living memory”. Unsurprisingly, given the accelerated nature of the transition to the new syllabus, minor ‘bumps in the road’, such as some early ‘programming friction’ had been encountered. However, the course was on track, aircraft availability was excellent, the syllabus and exercises were under constant review and development, and student feedback had been extremely positive.

When I return for Part 3 (next issue of MS&T), the course will have completed their final Capstone projects and be gearing up for graduation.


My first report on ETPS, “Learn to Test, Test to Learn” in Issue 2019-4/5 of MS&T ( provided a brief history and some background to the recent transformation of both the unit and the legacy course, specifically a major revision of the syllabus and teaching methods to comply with EASA qualification regulations, and the transfer of a significantly updated aircraft fleet from the military to the civil register.

ETPS formed in 1943 as part of the Aircraft and Armament Experimental Establishment (A&AEE), a military unit answering to the Air Ministry (later the Ministry of Defence (MoD) and collaborating closely with the Royal Aircraft Establishment (RAE) which became, in 1988, the Royal Aerospace Establishment. During the early 1990s, RAE and ETPS became part of the Defence Research Agency (DRA), later renamed the Defence Evaluation and Research Agency (DERA). In 2001 DERA was part-privatised by the MoD, resulting in two separate organisations, the state-owned Defence Science and Technology Laboratory (Dstl), and the privatised company QinetiQ.