There are multiple scores used for airway assesment ,the commonest one is LEMON score. LEMON is an airway assessment score that measures factors associated with difficult intubation such as obesity, head and neck movement, jaw movement , receding mandible, long upper incisors, Mallampatti scores, maxillary incisor characteristics, decreased mouth opening ,shorten thyromental distance and short neck.

The Height-to-Thyromental Distance ratio (H/TMD) has emerged as a simple, objective, and reproducible anatomical predictor of difficult laryngoscopy, as it normalizes mandibular space to patient height. However, airway difficulty is not purely anatomical; functional factors such as airway obstruction and cervical spine mobility significantly affect intubation success.

Therefore, combining H/TMD with two highly predictive functional elements from the LEMON score - Obstruction (O) and Neck Mobility (N) - may provide a more accurate, simplified, and clinically applicable model for predicting difficult airway. This combination is referred to as the HON Model (Height/TMD + Obstruction + Neck mobility).

Inclusion Criteria:

• Adult patients from 15- 60 yrs old
• Patients who require endotracheal intubation for surgery under general anesthesia.
• Patients with ASA I - II
• Patients who provide informed consent

Exclusion Criteria:

• Patients with history of previous difficult intubation.
• Patients with inability to sit/stand, heamodinamiclly unstable and need for rapid sequence induction .

The sample size calculation was performed using G. power 3.1.9.2 (Universitat Kiel, Germany) and total sample size will be 350. It was calculated according to a previous study (Pal et al., 2025, Rista et al., 2025) based the sensitivity of Height/Thyromental Distance Ratio and L.E.M.O.N score as to best of our knowledge our study will be the first to assess Height/Thyromental Distance Ratio Combined with Obstruction and Neck Mobility (HON Model) to predict difficult intubation (Power : 0.8, α error: 0.05).