Hardware in the loop simulation of helicopter PinS procedures using GLS avionics and an SBAS to GLS converter

Abstract

We designed and built a system intended to combine the advantages of both the ground based and the satellite-based augmentation systems (GBAS, SBAS) by using a converter between them. In both GBAS and SBAS, instant integrity information is provided by estimating protection levels, a high probability bound for the computed position. This is then compared to the alert limit of the respective system. Since both systems are quite similar, and the SBAS signal can nowadays be decoded even by low cost receivers, one can receive the augmentation data from the SBAS, slightly modify it to fit into the GBAS data structure and broadcast this data to a GBAS equipped aircraft. Said aircraft could execute an RNP approach with the Localizer Performance and Vertical guidance (LPV) final approach segment which would otherwise not be available. This may come especially handy in places where no non-precision minima are published, such as the RNP-E approach into Innsbruck and Salzburg, or where no other approach procedures are available to spatial or monetary constraints. Since there are slight differences between the two systems, we made sure that integrity for the safety-of-life approach service is ensured. We named the system GLASS (GLS Approaches using SbaS), built a prototype and began trials with real GBAS avionics hardware. To accomplish this, we created a hardware in the loop environment, which allows us to validate various receivers without having to go through a full flight certification of the hardware. We tested this environment using the DLR in house full motion rotorcraft simulator to fly point in space approaches during Helicopter Emergency Service (HEMS) missions. The test bench setup consists of an Orolia GSG5 GPS and SBAS simulator connected to both an SBAS receiver and a Funke Avionics GPU400 GLS receiver. The SBAS receiver is subsequently connected to a GLASS Station PC, which translates the SBAS corrections to GLS conformal structures and broadcasts them using a Telerad 9009 VDB GLS transmitter. This transmitter is also connected to the VHF data broadcast input of the GPU4000. The Orolia GSG5 receives data updates from the DLR flight simulator Aves (Figure 1). During the trials, the accuracy and integrity of both receivers behaved as expected. However, the Collins GLU925 showed an anomaly: if two corrections were broadcast with the same IODE parameter, the second one was ignored. This limits the availability of the system unnecessarily. Moreover, we found that both digital avionics devices did not evaluate the approach performance designator, one parameter of the final approach segment date block. This actually increases integrity while also limiting availability at the same time.