• Multi-domain characterization of instabilities in a liquid-fueled swirling combustor. • Flame analysis using POD, SPOD, and Cross-FFT to identify coherent structures. • Comparison between stable and unstable regimes (Φ = 0.36 and Φ = 0.18) highlighting low-frequency oscillations. • CMOS-compatible piezoelectric MEMS sensor for detecting structural vibrations. • Strong spectral coherence between accelerometer signals and flame dynamics. This work presents a multi-domain experimental characterization of combustion instabilities in a liquid-fueled swirling combustor operating with Jet-A1, combining high-speed optical imaging, dynamic pressure measurements, and structural vibration monitoring. Experiments were conducted at two global equivalence ratios (Φ = 0.36 and Φ = 0.18), representative of stable and ultra-lean unstable operating conditions. Flame dynamics were analyzed using Proper Orthogonal Decomposition (POD), Spectral POD (SPOD), and Cross-Fourier Transform (Cross-FFT), while pulsation mechanics were investigated through the Autocorrelation Function (ACF). Pressure fluctuations and structural vibrations were monitored using a commercial pressure sensor and an innovative uniaxial AlN-based piezoelectric MEMS accelerometer, fabricated via CMOS-compatible processes and characterized in terms of sensitivity, linearity, resonance, and hysteresis. Time-domain analysis revealed increased signal dispersion and intermittency at Φ = 0.18, while frequency-domain analysis showed that the MEMS accelerometer effectively captures transient components between 156 and 625 Hz, typical of turbulent combustion. Cross-spectral analysis demonstrated high coherence between accelerometer signals and dominant flame modes, highlighting the sensor’s capability to monitor structural dynamics and localized instabilities in real time. The results confirm that the MEMS accelerometer is a compact, non-intrusive, and reliable tool for real-time diagnostics of thermoacoustic instabilities, which can be integrated with optical and pressure measurements for advanced monitoring and control strategies. This combined approach offers valuable perspectives for developing advanced monitoring strategies and real-time control of gas turbine combustors.