LLM4AirTrack: LLM-Driven Multi-Feature Fusion for Aircraft Trajectory Prediction

Overview

LLM4AirTrack adapts the LLM4STP (Large Language Model for Ship Trajectory Prediction) framework from maritime AIS to aviation ADS-B domain. The core insight is that pre-trained LLMs encode powerful sequential pattern recognition that transfers to spatiotemporal trajectory data through lightweight reprogramming — without full fine-tuning.

The framework uses a frozen GPT-2 backbone with trainable adapter modules (~2.4% of total parameters) to predict future aircraft positions and classify flight routes/procedures.

Architecture

┌─────────────────────────────────────────────────────────────────┐
│                    LLM4AirTrack Framework                       │
│                                                                  │
│  ADS-B Features (9-dim: xyz + direction + polar)                │
│       │                                                          │
│       ▼                                                          │
│  ┌──────────────────┐                                           │
│  │ RevIN Normalizer  │  Instance normalization per feature       │
│  └──────────────────┘                                           │
│       │                                                          │
│       ▼                                                          │
│  ┌──────────────────┐                                           │
│  │ Patch Tokenizer   │  Overlapping temporal patches (8×9=72)   │
│  └──────────────────┘                                           │
│       │                                                          │
│       ▼                                                          │
│  ┌──────────────────┐   ┌─────────────────────┐                │
│  │ Patch Embedder    │   │ Text Prototype Bank  │                │
│  │ (72 → 768)        │   │ (256 learned protos) │                │
│  └──────────────────┘   └─────────────────────┘                │
│       │                         │                                │
│       ▼                         ▼                                │
│  ┌──────────────────────────────────────┐                       │
│  │  Cross-Attention Reprogrammer        │                       │
│  │  Q=patches, K=V=prototypes (8-head)  │                       │
│  │  Maps trajectory → LLM text space   │                       │
│  └──────────────────────────────────────┘                       │
│       │                                                          │
│       ▼                                                          │
│  ┌──────────────────┐                                           │
│  │ Prompt-as-Prefix  │  Aviation context prompt prepended       │
│  └──────────────────┘                                           │
│       │                                                          │
│       ▼                                                          │
│  ┌──────────────────┐                                           │
│  │  Frozen GPT-2     │  124M params frozen, language knowledge  │
│  └──────────────────┘                                           │
│       │                                                          │
│       ├──────────────────┐                                      │
│       ▼                  ▼                                      │
│  ┌──────────┐   ┌──────────────────┐                           │
│  │ Traj Head│   │ Classification   │                           │
│  │ (xyz)    │   │ Head (route/rwy) │                           │
│  └──────────┘   └──────────────────┘                           │
└─────────────────────────────────────────────────────────────────┘

Key Components

1. 9-Dimensional Kinematic Features (from ATSCC):

   • Position: (x, y, z) in East-North-Up coordinates
   • Directional unit vectors: (ux, uy, uz) — velocity direction
   • Polar components: (r, sin θ, cos θ) — angular position

2. Patch Tokenization: Overlapping temporal windows (patch_len=8, stride=4) → 14 patches from 60-step context

3. Cross-Attention Reprogramming (from Time-LLM): 256 learned text prototypes serve as a "translation dictionary" between trajectory and language domains

4. Frozen GPT-2 Backbone: 124M frozen parameters preserve pre-trained language understanding while keeping training efficient

5. Dual Output Heads:

   • Trajectory Prediction: Future (x, y, z) positions via Smooth L1 loss
   • Route Classification: STAR/IAF/Runway procedure via Cross-Entropy loss

Parameter Efficiency

Component	Parameters	Trainable
GPT-2 Backbone	124,439,808	0 (frozen)
Patch Embedder	57,600	57,600
Cross-Attention Reprogrammer	2,560,512	2,560,512
Trajectory Head	329,946	329,946
Classification Head	150,543	150,543
Total	127,543,059	3,103,251 (2.43%)

Training

Dataset

• Source: ATFMTraj — RKSIa (Incheon International Airport arrivals)
• Origin: OpenSky ADS-B recordings, 2018-2023
• Preprocessing: Raw lat/lon/alt → ENU coordinates → normalized to [-1,1] by r_max=120km
• Trajectories: 8,091 training + 8,092 test (16,183 total flights)
• Windows: 282,191 training + 20,000 evaluation sliding windows
• Context: 60 timesteps (1-second intervals = 1 minute of flight)
• Prediction: 30 timesteps ahead (30 seconds)
• Classes: 39 route labels (STAR × IAF × Runway combinations)

Hyperparameters

Parameter	Value
LLM Backbone	openai-community/gpt2 (768 hidden, 12 layers)
Optimizer	AdamW (β₁=0.9, β₂=0.999)
Learning Rate	5×10⁻⁴ with cosine annealing warm restarts
Weight Decay	1×10⁻⁵
Batch Size	128
Epochs	5
Gradient Clipping	max_norm=1.0
Multi-task Weight	λ_traj=1.0, λ_cls=0.1
Loss (trajectory)	Smooth L1 (Huber)
Loss (classification)	Cross-Entropy
Hardware	NVIDIA T4 (16GB VRAM, used ~1.4GB)

Results

Epoch	Train Loss	ADE	FDE	Route Accuracy
1	0.2335	0.01500	0.02047	34.7%
2	0.2110	0.01200	0.01635	36.1%
3	0.2033	0.01026	0.01426	36.3%
4	0.2037	0.01345	0.01858	34.9%
5	0.2003	0.01518	0.02043	36.5%

Best model (epoch 3):

• ADE: 0.01026 (normalized ENU scale; with r_max=120km → ~1.23km average displacement)
• FDE: 0.01426 (~1.71km final displacement error at 30s horizon)
• Route Classification: 36.3% accuracy over 39 classes (14× above random baseline of 2.6%)
• RMSE: x=0.00957, y=0.00942, z=0.00072 (altitude prediction is very accurate)

Usage

Quick Inference

import torch
import json
from huggingface_hub import hf_hub_download

# Download model files
config_path = hf_hub_download("Jdice27/LLM4AirTrack", "config.json")
weights_path = hf_hub_download("Jdice27/LLM4AirTrack", "adapter_weights.pt")

# You can use the self-contained train_full.py or the modular llm4airtrack package
from llm4airtrack.model import LLM4AirTrack

with open(config_path) as f:
    cfg = json.load(f)

model = LLM4AirTrack(
    llm_name=cfg["llm_name"],
    context_len=cfg["context_len"],
    pred_len=cfg["pred_len"],
    n_classes=cfg["n_classes"],
    n_prototypes=cfg["n_prototypes"],
    patch_len=cfg["patch_len"],
    patch_stride=cfg["patch_stride"],
)
state = torch.load(weights_path, map_location="cpu")
model.load_state_dict(state, strict=False)
model.eval()

# Input: 60 timesteps × 9 kinematic features
# Features: [x, y, z, ux, uy, uz, r, sin_θ, cos_θ] in ENU coordinates
context = torch.randn(1, 60, 9)  # Replace with real data
outputs = model(context, task="both")

future_xyz = outputs["pred_trajectory"]  # (1, 30, 3) — future ENU positions
route_probs = outputs["pred_class"].softmax(-1)  # (1, 39) — route probabilities

Data Pipeline

from llm4airtrack.data import download_atfm_dataset, load_atfm_raw, compute_kinematic_features

# Download and load ATFMTraj
download_atfm_dataset("RKSIa", cache_dir="./data")
data, labels = load_atfm_raw("RKSIa", "TEST", "./data")

# Get kinematic features for a single trajectory
traj = data[0]  # (T_max, 3) ENU coordinates
valid = ~np.isnan(traj[:, 0])
features = compute_kinematic_features(traj[valid])  # (T, 9)

Downstream Tasks

The model produces rich trajectory representations suitable for:

Task	How to Use
Track Activity Classification	Use pred_class output — identifies STAR/IAF/runway procedure
Trajectory Prediction	Use pred_trajectory — 30-second position forecast
Anomaly Detection	Compare pred_trajectory vs actual — large deviations flag anomalies
Conflict Detection	Run on multiple aircraft, check predicted trajectory intersections
ETA Prediction	Extract LLM hidden states as features for regression head
Transfer to New Airports	Fine-tune adapter weights on new airport data (ESSA, LSZH included in ATFMTraj)

Design Decisions & Adaptation from Maritime (LLM4STP) to Aviation (ADS-B)

Aspect	LLM4STP (Maritime AIS)	LLM4AirTrack (Aviation ADS-B)
Dimensionality	2D (lat, lon)	3D (lat, lon, altitude → ENU xyz)
Features	SOG, COG, ROT	Ground speed → directional vectors; vertical rate → uz
Update Rate	~10s intervals	1s intervals (higher resolution)
Route Structure	Free navigation	Defined STARs/SIDs (structured procedures)
Context	Port/strait proximity	Airport/procedure context (encoded in prompt)
Phase Segmentation	Anchoring/transiting	Climb/cruise/descent/approach
Classification	Vessel type	Route procedure (39 STAR×IAF×RWY classes)
Spatial Encoding	Lat/lon directly	ENU Cartesian + polar components

References

Foundational Work

• LLM4STP: GitHub — Original maritime trajectory prediction framework
• Time-LLM: arXiv 2310.01728 — LLM reprogramming for time series (ICLR 2024)

Aviation Domain

• ATSCC: arXiv 2407.20028 — Self-supervised trajectory representation, 9-dim feature engineering
• LLM4Delay: arXiv 2510.23636 — Cross-modality LLM for aviation delay prediction
• ATFMTraj: HuggingFace Dataset — Aircraft trajectory classification data

Related Approaches

• Flight2Vec: arXiv 2412.16581 — Behavior-adaptive patching for flight trajectories
• H3+CLM: arXiv 2405.09596 — Spatial tokenization for trajectory prediction
• SKETCH: arXiv 2601.18537 — Semantic key-point conditioning

Citation

@misc{llm4airtrack2026,
  title={LLM4AirTrack: LLM-Driven Multi-Feature Fusion for Aircraft Trajectory Prediction},
  author={Jdice27},
  year={2026},
  url={https://huggingface.co/Jdice27/LLM4AirTrack},
  note={Adapted from LLM4STP for aviation ADS-B domain}
}