PDU 39 Vietnam
For decades, the Aero L-39 Albatros has been one of the world’s most successful jet trainers. Yet as avionics standards evolved and digital cockpits became the new norm, the need for modern situational awareness tools — such as Head-Up Displays (HUDs) — became increasingly clear. SPEEL PRAHA took on the challenge of developing and integrating a full HUD system for various L-39 variants, bridging legacy design with contemporary mission capabilities.
From Feasibility to Flight Readiness
When SPEEL first began work on the PDU-39 project in 2010, the company had no prior experience developing HUD systems. What followed was a decade-long journey of research, prototyping, and system integration — a process that would ultimately position SPEEL among Europe’s few HUD manufacturers for military aviation.
“We had to walk a long and difficult path, filled with false starts and lessons learned,” recalls Petr Vidiečan, R&D Director at SPEEL PRAHA. “But those experiences became the foundation for the reliable and flexible system we have today.”
The development timeline was marked by distinct milestones:
- 2010–2015: Feasibility studies, technology demonstrators, and system definition in cooperation with AVA — gathering pilot feedback and evaluating various optical and display technologies.
- 2016–2018: Development of the PDU-39-02, the first serially produced HUD unit.
- 2018–2021: Flight testing and software refinement of the MP-39 mission computer that generates flight symbology.
- 2021: Military approval for operational use and start of serial production.
- 2022–2024: Development and qualification of the PDU-159-01, designed for the new L-39NG with a different cockpit geometry.
Compact Engineering for a Tight Cockpit
Integrating a modern HUD into a legacy airframe like the L-39 posed unique technical challenges. The original aircraft were never designed for such systems — they used a simple ASP-3NMU-39Z optical gunsight, with no provision for mounting a PDU.
SPEEL therefore developed a compact and lightweight display unit that fits within the L-39’s restricted space envelope while preserving the ejection trajectory and canopy clearance requirements.
By contrast, the L-39 SkyFox, designed from the outset to accommodate a HUD, allowed SPEEL to build a larger, higher-performance variant with improved viewing angles.
Digital Reliability and NVG Compatibility
Unlike older CRT-based systems, the PDU-39 uses a fully digital LED-driven architecture, providing exceptional image longevity and reliability. The design ensures crisp readability under all lighting conditions — a challenge often underestimated by non-pilots but critical for mission safety.
Compatibility with Night Vision Goggles (NVG) posed another major engineering hurdle. “The standard addressing NVG compatibility is extremely vague,” Vidiečan notes. “Achieving consistent performance across goggles from multiple manufacturers was a real puzzle.”
System Architecture
SPEEL’s HUD solution extends far beyond the display itself. The system includes:
- PDU (Head-Up Display Unit)
- MP (Mission Computer) generating real-time symbology
- MFD (Multi-Function Display) for the rear cockpit
- DVR (Data Video Recorder)
In total, eight interconnected units form a cohesive digital system supporting both training and operational missions.
The HUD-39 has already been delivered or contracted for 40+ aircraft across Kazakhstan, Ethiopia, Nigeria, and Vietnam, as well as 20+ SkyFox aircraft for CLV, HuAF, and current deliveries to Armenia.
Operational Benefits
The integration of a modern HUD transforms the L-39 training environment:
- Enhanced training realism – Enables advanced tactical exercises previously impossible without a HUD.
- Improved safety – Pilots maintain mission focus with critical data projected directly in their line of sight.
- Faster skill transfer – Trainees build habits consistent with modern fighter aircraft operations.
- Simplified maintenance – Digital architecture and LED sources reduce lifetime support costs.
- Customizable symbology – The MP-39 software allows rapid adaptation to customer-specific requirements.
“From a pilot’s perspective, the HUD changes everything,” adds Vidiečan. “It’s not just about seeing data — it’s about being able to fly the mission naturally, safely, and effectively.”
By: Katerina Urbanova
Photo Credit: SPEEL Praha
